{{Short description|Subdiscipline of chemistry, focusing on carbon compounds}}
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{{TopicTOC-Chemistry}}
'''Organic chemistry''' is a [[subdiscipline]] within [[chemistry]] involving the [[science|scientific]] study of the structure, properties, and reactions of [[organic compound]]s and [[organic matter|organic materials]] (i.e. [[matter]] in its various forms that contain [[carbon]] [[atom]]s).<ref name="J. Clayden, N. Greeves 2012 pp. 1-15">Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. {{ISBN|0-19-927029-5}}.</ref> It involves studying the structure of organic material to determine the [[structural formula]], analyzing [[Physical property|physical]] and [[Chemical property|chemical properties]], and evaluating [[Reactivity (chemistry)|chemical reactivity]] to understand the behavior of organic compounds. The study of [[organic reaction]]s includes the [[organic synthesis|chemical synthesis]] of [[natural product]]s, [[drug]]s, and [[polymer]]s, and study of individual organic [[molecule]]s in the laboratory and via theoretical ([[in silico]]) study.

The range of chemicals studied {{not a typo|in organic}}<!-- don't 'correct' to "inorganic" --> chemistry includes [[hydrocarbon]]s (compounds containing only [[carbon]] and [[hydrogen]]) as well as compounds based on carbon, but also containing other elements,<ref name="J. Clayden, N. Greeves 2012 pp. 1-15" /><ref>Morrison, Robert T.; Boyd, Robert N. and Boyd, Robert K. (1992) ''Organic Chemistry'', 6th ed., Benjamin Cummings. {{ISBN|978-0136436690}}.</ref> especially [[oxygen]], [[nitrogen]], [[sulfur]], [[phosphorus]] (included in many [[biochemicals]]) and the [[halogen]]s. [[Organometallic chemistry]] is the study of compounds containing carbon–[[metal]] bonds.<ref>Elschenbroich, C. (2006) ''Organometallics'' 3rd Ed., Wiley-VCH</ref>

Organic compounds form the basis of all [[carbon-based life|known life]] and constitute the majority of known chemicals. The bonding patterns of carbon, with its [[valence (chemistry)|valence]] of four—formal single, double, and triple bonds, plus structures with [[Delocalized electron|delocalized electrons]]—make the array of organic compounds structurally diverse, and their range of applications enormous. They form the basis of, or are constituents of, many commercial products including [[drug|pharmaceuticals]]; [[petrochemical]]s and [[agrichemical]]s, and products made from them including [[lubricants]], [[solvents]]; [[plastic]]s; [[fuels]] and [[explosive material|explosives]]. The study of organic chemistry overlaps [[organometallic chemistry]] and [[biochemistry]], but also with [[medicinal chemistry]], [[polymer chemistry]], and [[materials science]].<ref name="J. Clayden, N. Greeves 2012 pp. 1-15"/>

==Educational aspects==
Organic chemistry is typically taught at the college or university level.<ref>{{Cite journal |last1=Blackie |first1=Margaret A.L. |last2=Arnott |first2=Gareth |last3=Kaschula |first3=Catherine H. |date=2023-09-12 |title=Engaging Organic Chemistry Students in Knowledge Building |journal=Journal of Chemical Education |language=en |volume=100 |issue=9 |pages=3302–3308 |doi=10.1021/acs.jchemed.2c00980 |issn=0021-9584|doi-access=free |bibcode=2023JChEd.100.3302B }}</ref> It is considered a very challenging course but has also been made accessible to students.<ref>{{Cite journal |last=Holme |first=Thomas A. |date=2023-06-13 |title=A Snapshot of Organic Chemistry Instruction and Curriculum over the Past 100 Years |journal=Journal of Chemical Education |language=en |volume=100 |issue=6 |pages=2093–2095 |doi=10.1021/acs.jchemed.3c00467 |issn=0021-9584|doi-access=free |bibcode=2023JChEd.100.2093H }}</ref>

==History==
{{Main|History of chemistry}}
{{For timeline|Timeline of biology and organic chemistry}}
[[Image:Friedrich woehler.jpg|upright|thumb|[[Friedrich Wöhler]]]]
Before the 18th century, [[chemist]]s generally believed that [[Chemical compound|compounds]] obtained from living organisms were endowed with a vital force that distinguished them from [[inorganic compound]]s. According to the concept of [[vitalism]] (vital force theory), organic matter was endowed with a "vital force".<ref name=G%E>{{Greenwood&Earnshaw2nd}}</ref> During the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 [[Michel Eugène Chevreul|Michel Chevreul]] started a study of [[soap]]s made from various [[fat]]s and [[alkali]]s. He separated the acids that, in combination with the alkali, produced the soap. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats (which traditionally come from organic sources), producing new compounds, without "vital force". In 1828 [[Friedrich Wöhler]] produced the ''organic'' chemical [[urea]] (carbamide), a constituent of [[urine]], from ''inorganic'' starting materials (the salts [[potassium cyanate]] and [[ammonium sulfate]]), in what is now called the [[Wöhler synthesis]]. Although Wöhler himself was cautious about claiming he had disproved vitalism, this was the first time a substance thought to be organic was synthesized in the laboratory without biological (organic) starting materials. The event is now generally accepted as indeed disproving the doctrine of vitalism.<ref>{{cite book|title=A Source Book in Chemistry, 1400-1900|author=Henry Marshall Leicester|author2=Herbert S. Klickstein|publisher=Harvard University Press|date=1951|page=309}}</ref>

After Wöhler, [[Justus von Liebig]] worked on the organization of organic chemistry, being considered one of its principal founders.<ref name=RoyalSocietyObit>{{cite journal|last1=Royal Society of London|title=Obituary Notices of Fellows Deceased|journal=Proceedings of the Royal Society of London|date=1 January 1875|volume=24|pages=xxvii–xxxvii|bibcode=1875RSPS...24D...1. |url=https://archive.org/stream/philtrans06902924/06902924#page/n25/mode/2up/search/Liebig|access-date=5 November 2014}}</ref>

In 1856, [[Sir William Henry Perkin|William Henry Perkin]], while trying to manufacture [[quinine]], accidentally produced the organic [[dye]] now known as [[Perkin's mauve]]. His discovery, made widely known through its financial success, greatly increased interest in organic chemistry.<ref>{{cite journal|author=Kiefer, D. M. |title=Organic Chemicals' Mauve Beginning|journal= Chem. Eng. News |year=1993|volume=71|issue=32|pages=22–23|doi=10.1021/cen-v071n032.p022}}</ref>

A crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently in 1858 by both [[Friedrich August Kekulé]] and [[Archibald Scott Couper]].<ref name=KekuleCHF>{{cite web|title=August Kekulé and Archibald Scott Couper|url=https://www.sciencehistory.org/historical-profile/august-kekul%C3%A9-and-archibald-scott-couper|website=[[Science History Institute]]|access-date=20 March 2018|date=June 2016|archive-date=21 March 2018|archive-url=https://web.archive.org/web/20180321132315/https://www.sciencehistory.org/historical-profile/august-kekul%C3%A9-and-archibald-scott-couper|url-status=dead}}</ref> Both researchers suggested that [[valence (chemistry)|tetravalent]] carbon atoms could link to each other to form a carbon lattice, and that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.<ref name=":0">{{Cite book |last1=Streitwieser |first1=Andrew |title=Introduction to Organic Chemistry |last2=Heathcock |first2=Clayton H. |last3=Kosower |first3=Edward M. |publisher=Medtech (Scientific International, reprint of revised 4th edition, Macmillan, 1998) |year=2017 |isbn=978-93-85998-89-8 |location=New Delhi |pages=3–4}}</ref>

The era of the [[pharmaceutical]] industry began in the last decade of the 19th century when the German company, [[Bayer]], first manufactured acetylsalicylic acid—more commonly known as [[aspirin]].<ref>Roberts, Laura (7 December 2010) [https://web.archive.org/web/20101218090457/http://www.telegraph.co.uk/health/healthnews/8184625/History-of-aspirin.html History of Aspirin]. ''The Telegraph''</ref> By 1910 [[Paul Ehrlich]] and his laboratory group began developing arsenic-based [[arsphenamine]] (Salvarsan) as the first effective medicinal treatment of [[syphilis]], and thereby initiated the medical practice of [[chemotherapy]]. Ehrlich popularized the concepts of "magic bullet" drugs and of systematically improving drug therapies.<ref name=BoschRosich>{{cite journal |doi=10.1159/000149583 |title=The contributions of Paul Ehrlich to pharmacology: A tribute on the occasion of the centenary of his Nobel Prize |year=2008 |author1=Bosch F |author2=Rosich L |journal=Pharmacology |volume=82 |issue=3 |pages=171–9 |pmid=18679046 |pmc=2790789}}</ref><ref>{{cite web |publisher=Rockefeller University |url=http://centennial.rucares.org/index.php?page=Chemotherapy |title=Paul Ehrlich, the Rockefeller Institute, and the first targeted chemotherapy |access-date=3 Aug 2012}}</ref> His laboratory made decisive contributions to developing antiserum for [[diphtheria]] and standardizing therapeutic serums.<ref name="CHF">{{cite web|title=Paul Ehrlich|url=https://www.sciencehistory.org/historical-profile/paul-ehrlich|website=Science History Institute|access-date=20 March 2018|date=June 2016}}</ref>

[[File:Cefalotin.svg|thumb|[[Cefalotin]] is a widely used synthetic [[antibiotic]].<ref name="Vardanyan_2006">{{cite book |doi=10.1016/B978-044452166-8/50032-7 |chapter=Antibiotics |title=Synthesis of Essential Drugs |date=2006 | vauthors = Vardanyan R, Hruby V |pages=425–498 |isbn=978-0-444-52166-8 }}</ref>]]

Early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds. The development of [[synthetic indigo]] is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the synthetic methods developed by [[Adolf von Baeyer]]. In 2002, 17,000 tons of synthetic indigo were produced from [[petrochemical]]s.<ref name=Ullmann>Steingruber, Elmar (2004) "Indigo and Indigo Colorants" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. {{doi| 10.1002/14356007.a14_149.pub2}}</ref>

In the early part of the 20th century, [[polymer]]s and [[enzyme]]s were shown to be large organic molecules, and petroleum was shown to be of biological origin.

The multiple-step synthesis of complex organic compounds is called total synthesis. [[Total synthesis]] of complex natural compounds increased in complexity to [[glucose]] and [[terpineol]]. For example, [[cholesterol]]-related compounds have opened ways to synthesize complex [[List of human hormones|human hormones]] and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as [[lysergic acid]] and [[vitamin B12|vitamin B<sub>12</sub>]].<ref>{{cite book |author1= Nicolaou, K.C. |author2= Sorensen, E.J. |title= Classics in Total Synthesis: Targets, Strategies, Methods |publisher= [[John Wiley & Sons|Wiley]] |year= 1996 | isbn= 978-3-527-29231-8 }}</ref>
[[image:Cyanocobalamin.svg|thumb|left|230px|The [[total synthesis]] of vitamin B<sub>12</sub> marked a major achievement in organic chemistry.]]

The discovery of [[petroleum]] and the development of the [[petrochemical industry]] spurred the development of organic chemistry. Converting individual petroleum compounds into ''types'' of compounds by various chemical processes led to [[organic reactions]] enabling a broad range of industrial and commercial products including, among (many) others: [[plastics]], [[synthetic rubber]], organic [[adhesives]], and various property-modifying petroleum additives and [[Catalysis|catalysts]].

The majority of chemical compounds occurring in biological organisms are carbon compounds, so the association between organic chemistry and [[biochemistry]] is so close that biochemistry might be regarded as in essence a branch of organic chemistry. Although the [[history of biochemistry]] might be taken to span some four centuries, fundamental understanding of the field only began to develop in the late 19th century and the actual term ''biochemistry'' was coined around the start of 20th century. Research in the field increased throughout the twentieth century, without any indication of slackening in the rate of increase, as may be verified by inspection of abstraction and indexing services such as [[BIOSIS Previews]] and [[Biological Abstracts]], which began in the 1920s as a single annual volume, but has grown so drastically that by the end of the 20th century it was only available to the everyday user as an online electronic [[database]].<ref>Allan, Barbara. Livesey, Brian (1994). ''How to Use Biological Abstracts, Chemical Abstracts and Index Chemicus''. Gower. {{ISBN|978-0-566-07556-8}}</ref>

== Characterization ==
Since organic compounds often exist as [[mixture]]s, a variety of techniques have also been developed to assess purity; [[chromatography]] techniques are especially important for this application, and include [[High-performance liquid chromatography|HPLC]] and [[gas chromatography]]. Traditional methods of separation include [[distillation]], [[crystallization]], [[evaporation]], [[magnetic separation]] and [[solvent extraction]].

Organic compounds were traditionally characterized by a variety of chemical tests, called "wet methods", but such tests have been largely displaced by spectroscopic or other computer-intensive methods of analysis.<ref>Shriner, R.L.; Hermann, C.K.F.; Morrill, T.C.; Curtin, D.Y. and Fuson, R.C. (1997) ''The Systematic Identification of Organic Compounds''. John Wiley & Sons, {{ISBN|0-471-59748-1}}</ref> Listed in approximate order of utility, the chief analytical methods are:
* [[Nuclear magnetic resonance|Nuclear magnetic resonance (NMR) spectroscopy]] is the most commonly used technique, often permitting the complete assignment of atom connectivity and even stereochemistry using [[correlation spectroscopy]]. The principal constituent atoms of organic chemistry – hydrogen and carbon – exist naturally with NMR-responsive isotopes, respectively <sup>1</sup>H and <sup>13</sup>C.
* [[Elemental analysis]]: A destructive method used to determine the elemental composition of a molecule. See also mass spectrometry, below.
* [[Mass spectrometry]] indicates the [[molecular weight]] of a compound and, from the [[mass spectrum analysis|fragmentation patterns]], its structure. High-resolution mass spectrometry can usually identify the exact formula of a compound and is used in place of elemental analysis. In former times, mass spectrometry was restricted to neutral molecules exhibiting some volatility, but advanced ionization techniques allow one to obtain the "mass spec" of virtually any organic compound.
* [[Crystallography]] can be useful for determining [[molecular geometry]] when a single crystal of the material is available. Highly efficient hardware and software allows a structure to be determined within hours of obtaining a suitable crystal.

Traditional spectroscopic methods such as [[infrared spectroscopy]], [[optical rotation]], and [[UV/VIS spectroscopy]] provide relatively nonspecific structural information but remain in use for specific applications. Refractive index and density can also be important for substance identification.

== Properties ==
The physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information includes a melting point, boiling point, solubility, and index of refraction. Qualitative properties include odor, consistency, and color.

=== Melting and boiling properties ===
Organic compounds typically melt and many boil. In contrast, while inorganic materials generally can be melted, many do not boil, and instead tend to degrade. In earlier times, the melting point (m.p.) and boiling point (b.p.) provided crucial information on the purity and identity of organic compounds. The melting and boiling points correlate with the polarity of the molecules and their molecular weight. Some organic compounds, especially symmetrical ones, [[Sublimation (phase transition)|sublime]]. A well-known example of a sublimable organic compound is [[1,4-Dichlorobenzene|''para''-dichlorobenzene]], the odiferous constituent of modern mothballs. Organic compounds are usually not very stable at temperatures above 300&nbsp;°C, although some exceptions exist.

===Solubility===
Neutral organic compounds tend to be [[hydrophobic]]; that is, they are less [[soluble]] in water than in organic solvents. Exceptions include organic compounds that contain [[ionizable]] groups as well as low [[molecular weight]] [[Alcohol (chemistry)|alcohol]]s, [[amine]]s, and [[carboxylic acid]]s where [[hydrogen bonding]] occurs. Otherwise, organic compounds tend to dissolve in organic [[solvent]]s. Solubility varies widely with the organic solute and with the organic solvent.

===Solid state properties===

Various specialized properties of [[Molecular solid|molecular crystals]] and [[Polymer|organic polymers]] with [[conjugated system]]s are of interest depending on applications, e.g. thermo-mechanical and electro-mechanical such as [[piezoelectricity]], electrical conductivity (see [[conductive polymer]]s and [[organic semiconductor]]s), and electro-optical (e.g. [[non-linear optics]]) properties. For historical reasons, such properties are mainly the subjects of the areas of [[polymer science]] and [[materials science]].

== Nomenclature ==
{{Main|IUPAC nomenclature of organic chemistry}}
[[Image:OrgNom.svg|thumb|center|760px| Various names and depictions for one organic compound]]

The names of organic compounds are either systematic, following logically from a set of rules, or nonsystematic, following various traditions. Systematic nomenclature is stipulated by specifications from [[IUPAC]] (International Union of Pure and Applied Chemistry). Systematic nomenclature starts with the name for a [[parent structure]] within the molecule of interest. This parent name is then modified by prefixes, suffixes, and numbers to unambiguously convey the structure. Given that millions of organic compounds are known, rigorous use of systematic names can be cumbersome. Thus, IUPAC recommendations are more closely followed for simple compounds, but not complex molecules. To use the systematic naming, one must know the structures and names of the parent structures. Parent structures include unsubstituted hydrocarbons, heterocycles, and monofunctionalized derivatives thereof.

Nonsystematic nomenclature is simpler and unambiguous, at least to organic chemists. Nonsystematic names do not indicate the structure of the compound. They are common for complex molecules, which include most natural products. Thus, the informally named [[lysergic acid diethylamide]] is systematically named
(6a''R'',9''R'')-''N'',''N''-diethyl-7-methyl-4,6,6a,7,8,9-hexahydroindolo-[4,3-''fg''] quinoline-9-carboxamide.

With the increased use of computing, other naming methods have evolved that are intended to be interpreted by machines. Two popular formats are [[SMILES]] and [[InChI]].

===Structural drawings===
Organic molecules are described more commonly by drawings or [[structural formula]]s, combinations of drawings and chemical symbols. The [[Bond-line formula|line-angle formula]] is simple and unambiguous. In this system, the endpoints and intersections of each line represent one carbon, and hydrogen atoms can either be notated explicitly or assumed to be present as implied by [[Tetravalence|tetravalent]] carbon.
[[File:Stuctural drawings of butane 854px.jpg|alt=Structural representations of butane|thumb|center|upright=3.5|This diagram shows 5 distinct structural representations of the organic compound butane. The left-most structure is a bond-line drawing where the hydrogen atoms are removed. The second structure shows the added hydrogens depicted—the dark wedged bonds indicate the hydrogen atoms are coming toward the reader, the hashed bonds indicate the atoms are oriented away from the reader, and the solid (plain) bonds indicate the bonds are in the plane of the screen/paper. The middle structure shows the four carbon atoms. The 4th structure is a representation just showing the atoms and bonds without three dimensions. The right-most structure is a condensed structure representation of butane.]]

===History===
By 1880 an explosion in the number of chemical compounds being discovered occurred, assisted by new synthetic and analytical techniques. Grignard described the situation as "chaos le plus complet" (complete chaos) due to the lack of convention, it was possible to have multiple names for the same compound. This led to the creation of the [[Geneva Rules|Geneva rules]] in 1892.<ref>{{Cite journal|last=Evieux|first=E. A.|date=1954-06-01|title=The Geneva Congress on Organic Nomenclature, 1892|journal=Journal of Chemical Education|volume=31|issue=6|pages=326|doi=10.1021/ed031p326|issn=0021-9584|bibcode=1954JChEd..31..326E}}</ref>

==Classification of organic compounds==

===Functional groups===
[[Image:Acetic acid atoms.svg|upright|thumb|The family of [[carboxylic acid]]s contains a carboxyl (-COOH) [[functional group]]. [[Acetic acid]], shown here, is an example.]]
{{Main|Functional group}}

The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties. A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified based on their functional groups. Alcohols, for example, all have the subunit C-O-H. All alcohols tend to be somewhat [[hydrophile|hydrophilic]], usually form [[ester]]s, and usually can be converted to the corresponding [[halide]]s. Most functional groups feature heteroatoms (atoms other than C and H). Organic compounds are classified according to functional groups, e.g., alcohols, carboxylic acids, amines, etc.<ref name=March>{{March6th}}</ref> Functional groups make the molecule more acidic or basic due to their electronic influence on surrounding parts of the molecule.

As the [[Acid dissociation constant|p''K<sub>a</sub>'']] (aka [[Base (chemistry)|basicity]]) of the molecular addition/functional group increases, there is a corresponding [[dipole]], when measured, increases in strength. A dipole directed towards the functional group (higher p''K<sub>a</sub>'' therefore basic nature of group) points towards it and decreases in strength with increasing distance. Dipole distance (measured in [[Angstrom]]s) and [[Steric effects|steric hindrance]] towards the functional group have an intermolecular and intramolecular effect on the surrounding environment and [[pH]] level.

Different functional groups have different p''K<sub>a</sub>'' values and bond strengths (single, double, triple) leading to increased electrophilicity with lower p''K<sub>a</sub>'' and increased nucleophile strength with higher p''K<sub>a</sub>''. More basic/nucleophilic functional groups desire to attack an electrophilic functional group with a lower p''K<sub>a</sub>'' on another molecule (intermolecular) or within the same molecule (intramolecular). Any group with a net acidic p''K<sub>a</sub>'' that gets within range, such as an acyl or carbonyl group is fair game. Since the likelihood of being attacked decreases with an increase in p''K<sub>a</sub>'', [[acyl chloride]] components with the lowest measured [[PKa|p''K<sub>a</sub>'']] values are most likely to be attacked, followed by carboxylic acids (p''K<sub>a</sub>'' = 4), thiols (13), malonates (13), alcohols (17), aldehydes (20), nitriles (25), esters (25), then amines (35).<ref>{{Cite web|date=2010-06-18|title=The pKa Table Is Your Friend|url=https://www.masterorganicchemistry.com/2010/06/18/know-your-pkas/|access-date=2021-03-16|website=Master Organic Chemistry|language=en-US}}</ref> Amines are very basic, and are great nucleophiles/attackers.

===Aliphatic compounds===
{{Main|Aliphatic compound}}
The aliphatic hydrocarbons are subdivided into three groups of [[homologous series]] according to their state of [[Saturated and unsaturated compounds|saturation]]:
* [[alkanes]] (paraffins): aliphatic hydrocarbons without any [[Double bond|double]] or [[triple bond]]s, i.e. just C-C, C-H single bonds
* [[alkenes]] (olefins): aliphatic hydrocarbons that contain one or more double bonds, i.e. di-olefins (dienes) or poly-olefins.
* [[alkynes]] (acetylenes): aliphatic hydrocarbons which have one or more triple bonds.
The rest of the group is classified according to the functional groups present. Such compounds can be "straight-chain", branched-chain or cyclic. The degree of branching affects characteristics, such as the [[octane number]] or [[cetane number]] in petroleum chemistry.

Both saturated ([[alicyclic]]) compounds and unsaturated compounds exist as cyclic derivatives. The most stable rings contain five or six carbon atoms, but large rings (macrocycles) and smaller rings are common. The smallest cycloalkane family is the three-membered [[cyclopropane]] ((CH<sub>2</sub>)<sub>3</sub>). Saturated cyclic compounds contain single bonds only, whereas aromatic rings have an alternating (or conjugated) double bond. [[Cycloalkane]]s do not contain multiple bonds, whereas the [[cycloalkene]]s and the [[cycloalkyne]]s do.

===Aromatic compounds===
[[Image: Benzene-resonance-structures.svg|right|thumb|[[Benzene]] is one of the best-known aromatic compounds as it is one of the simplest and most stable aromatics.]]
[[Aromatic]] hydrocarbons contain [[Conjugated system|conjugated]] double bonds. This means that every carbon atom in the ring is sp<sup>2</sup> hybridized, allowing for added stability. The most important example is [[benzene]], the structure of which was formulated by [[Friedrich August Kekulé von Stradonitz|Kekulé]] who first proposed the [[Delocalized electron|delocalization]] or [[Resonance (chemistry)|resonance]] principle for explaining its structure. For "conventional" cyclic compounds, aromaticity is conferred by the presence of 4n + 2 delocalized pi electrons, where n is an integer. Particular instability ([[antiaromaticity]]) is conferred by the presence of 4n conjugated pi electrons.

===Heterocyclic compounds===
{{Main|Heterocyclic compound}}
The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a [[heterocycle]]. [[Pyridine]] and [[furan]] are examples of aromatic heterocycles while [[piperidine]] and [[tetrahydrofuran]] are the corresponding [[alicyclic]] heterocycles. The heteroatom of heterocyclic molecules is generally oxygen, sulfur, or nitrogen, with the latter being particularly common in biochemical systems.

Heterocycles are commonly found in a wide range of products including aniline dyes and medicines. Additionally, they are prevalent in a wide range of biochemical compounds such as [[alkaloids]], vitamins, steroids, and nucleic acids (e.g. DNA, RNA).

Rings can fuse with other rings on an edge to give [[polycyclic compound]]s. The [[purine]] nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed ''[[spiro compound|spiro]]'' and are important in several [[natural product]]s.

=== Polymers ===
{{Main|Polymer}}
[[Image: Girl with swimming board.jpg|upright|thumb|This swimming board is made of [[polystyrene]]; it is an example of a polymer.]]

One important property of carbon is that it readily forms chains, or networks, that are linked by carbon-carbon (carbon-to-carbon) bonds. The linking process is called [[polymerization]], while the chains, or networks, are called [[polymer]]s. The source compound is called a [[monomer]].

Two main groups of polymers exist: [[synthetic polymers]] and [[biopolymer]]s. Synthetic polymers are artificially manufactured, and are commonly referred to as [[plastic|industrial polymers]].<ref>"industrial polymers, chemistry of." [[Encyclopædia Britannica]]. 2006</ref> Biopolymers occur within a respectfully natural environment, or without human intervention.

===Biomolecules===
[[Image:Maitotoxin 2D structure.svg|thumb|upright=2|[[Maitotoxin]], a complex organic biological toxin]]
[[Biomolecule|Biomolecular chemistry]] is a major category within organic chemistry which is frequently studied by [[biochemists]]. Many complex multi-functional group molecules are important in living organisms. Some are long-chain [[biopolymer]]s, and these include [[peptides]], [[DNA]], [[RNA]] and the [[polysaccharide]]s such as [[starch]]es in animals and [[cellulose]]s in plants. The other main classes are [[amino acid]]s (monomer building blocks of peptides and proteins), [[carbohydrate]]s (which includes the polysaccharides), the [[nucleic acid]]s (which include DNA and RNA as polymers), and the [[lipid]]s. Besides, animal biochemistry contains many small molecule intermediates which assist in energy production through the [[Krebs cycle]], and produces [[isoprene]], the most common hydrocarbon in animals. Isoprenes in animals form the important [[steroid]] structural ([[cholesterol]]) and steroid hormone compounds; and in plants form [[terpene]]s, [[terpenoid]]s, some [[alkaloid]]s, and a class of hydrocarbons called biopolymer polyisoprenoids present in the [[latex]] of various species of plants, which is the basis for making [[rubber]]. Biologists usually classify the above-mentioned biomolecules into four main groups, i.e., proteins, lipids, carbohydrates, and nucleic acids. Petroleum and its derivatives are considered organic molecules, which is consistent with the fact that this oil comes from the fossilization of living beings, i.e., biomolecules.<ref>{{cite web |last1=Meinschein (2) |first1=W. G. |title=Origin of Petroleum |url=https://archives.datapages.com/data/bulletns/1957-60/data/pg/0043/0005/0900/0925.htm |website=AAPG.org |access-date=3 May 2024}}</ref>
See also: [[peptide synthesis]], [[oligonucleotide synthesis]] and [[carbohydrate synthesis]].

=== Small molecules ===
[[File:Cafeïne.png|right|thumb|Molecular models of [[caffeine]]]]
In pharmacology, an important group of organic compounds is [[small molecule]]s, also referred to as "small organic compounds". In this context, a small molecule is a small organic compound that is biologically active but is not a [[polymer]]. In practice, small molecules have a [[molar mass]] less than approximately 1000 g/mol.

=== Fullerenes ===

[[Fullerene]]s and [[carbon nanotube]]s, carbon compounds with spheroidal and tubular structures, have stimulated much research into the related field of [[materials science]]. The first fullerene was discovered in 1985 by Sir Harold W. Kroto of the United Kingdom and by Richard E. Smalley and Robert F. Curl Jr., of the United States. Using a laser to vaporize graphite rods in an atmosphere of helium gas, these chemists and their assistants obtained cagelike molecules composed of 60 carbon atoms (C60) joined by single and double bonds to form a hollow sphere with 12 pentagonal and 20 hexagonal faces—a design that resembles a football, or soccer ball. In 1996 the trio was awarded the Nobel Prize for their pioneering efforts. The C60 molecule was named [[buckminsterfullerene]] (or, more simply, the buckyball) after the American architect [[Buckminster Fuller|R. Buckminster Fuller]], whose geodesic dome is constructed on the same structural principles.

=== Others ===
Organic compounds containing bonds of carbon to nitrogen, oxygen and the halogens are not normally grouped separately. Others are sometimes put into major groups within organic chemistry and discussed under titles such as [[organosulfur chemistry]], [[organometallic chemistry]], [[organophosphorus chemistry]] and [[Organosilicon|organosilicon chemistry]].

== Organic reactions ==
{{Main|Organic reaction}}
[[Organic reaction]]s are [[chemical reaction]]s involving [[organic compound]]s.<ref name=March/> Many of these reactions are associated with functional groups. The general theory of these reactions involves careful analysis of such properties as the [[electron affinity]] of key atoms, [[bond strength]]s and [[steric hindrance]]. These factors can determine the relative stability of short-lived [[reactive intermediate]]s, which usually directly determine the path of the reaction.

The basic reaction types are: [[addition reaction]]s, [[elimination reaction]]s, [[substitution reaction]]s, [[pericyclic reaction]]s, rearrangement reactions and [[Redox|redox reactions]].<ref name=March/> An example of a common reaction is a [[substitution reaction]] written as:

:{{chem2 | Nu-  +  C\sX  -> C\sNu + X- }}

where X is some [[functional group]] and Nu is a [[nucleophile]].

The number of possible organic reactions is infinite. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens in sequence—although the detailed description of steps is not always clear from a list of reactants alone.

The stepwise course of any given reaction mechanism can be represented using [[arrow pushing]] techniques in which curved arrows are used to track the movement of electrons as starting materials transition through intermediates to final products. The mechanism for certain organic reactions remain subjects of ongoing debate and have not been fully elucidated.<ref>{{Cite journal |last=Croll |first=Elizabeth A. |last2=Kwon |first2=Ohyun |date=June 2024 |title=Mechanism of the Mitsunobu Reaction: An Ongoing Mystery |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC11661848/ |journal=Synthesis |volume=56 |issue=12 |pages=1843–1850 |doi=10.1055/a-2232-8633 |issn=0039-7881 |pmc=11661848 |pmid=39711915}}</ref>

== Organic synthesis ==
[[Image:Corey oseltamivir synthesis.png|thumb|upright=1.75|A synthesis designed by [[E.J. Corey]] for [[oseltamivir]] (Tamiflu). This synthesis has 11 distinct reactions.]]
{{see also|Chemical synthesis|Organic synthesis}}
Synthetic organic chemistry is an [[applied science]] as it borders [[engineering]], the "design, analysis, and/or construction of works for practical purposes".<ref>{{Cite book |title=Organic Synthesis |url=https://www.sciencedirect.com/book/9780128007204/organic-synthesis |access-date=2024-10-25 |isbn=978-0-12-800720-4 |language=en}}</ref> Organic synthesis of a novel compound is a problem-solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a [[carbonyl]] compound can be used as a [[nucleophile]] by converting it into an [[enolate]], or as an [[electrophile]]; the combination of the two is called the [[aldol reaction]]. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called [[total synthesis]].<ref name=March/>

Strategies to design a synthesis include [[retrosynthesis]], popularized by [[E.J. Corey]], which starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed because each compound and also each precursor has multiple syntheses.

==See also==
{{Main|Outline of organic chemistry}}
* [[List of important publications in chemistry#Organic chemistry|Important publications in organic chemistry]]
* [[List of organic reactions]]
* [[Molecular modelling]]

==References==
{{reflist|30em}}

==External links==
{{Wikiversity department}}
{{Wikibooks}}
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{{Commons category}}
* [http://ocw.mit.edu/courses/chemistry/5-12-organic-chemistry-i-spring-2005/ MIT.edu], OpenCourseWare: Organic Chemistry I
* [http://www.haverford.edu/wintnerorganicchem Haverford.edu], Organic Chemistry Lectures, Videos and Text
* [https://www.organic-chemistry.org Organic-Chemistry.org], Organic Chemistry Portal – Recent Abstracts and (Name)Reactions
* [https://orgsyn.org Orgsyn.org], Organic Chemistry synthesis journal
* [https://www.pearson.com/channels/organic-chemistry Pearson Channels], Organic Chemistry Video Lectures and Practice Problems
* [https://www.khanacademy.org/science/organic-chemistry Khanacademy.org], [[Khan Academy]] - Organic Chemistry
* [https://www.taylorfrancis.com/books/oa-mono/10.1201/9781003479352/organic-chemistry-william-tucker Organic Chemistry: Structure, Function, and Practice by William Tucker]
* [https://openoregon.pressbooks.pub/introductoryorganic/ Introductory Organic Chemistry by Carol Higginbotham]

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[[Category:Chemistry]]
[[Category:Organic compounds|Chemistry]]