Organic chemistry is the scientific study of the structures, properties, and methods of syntheses of chemical compounds that are based on carbon. This field stands in a complementary relationship to inorganic chemistry, which covers the study of the compounds of all other elements, as well as the elements themselves. These two disciplines are generally considered separately, but there is much overlap, such as in the sub-discipline of organometallic chemistry.
Organic compounds are primarily composed of carbon and hydrogen, and may contain any number of other elements, the most common of which are nitrogen and oxygen. Each carbon atom, with its pattern of forming four covalent bonds, can connect with other carbon atoms in a variety of ways to give the enormous diversity of organic compounds found. Each molecule is often described as having a "skeleton" of carbon atoms. The essential indication for existence and relationship inherent in four-based structures is appropriate for carbon, as it is one of the bases of life itself.
Important classes of organic compounds include the alkanes, alkenes, alkynes, aromatic compounds, alcohols, aldehydes, ketones, carboxylic acids, esters, ethers, amines, and amides. Many organic compounds—such as carbohydrates, amino acids, proteins, lipids, nucleotides, and nucleic acids—are found in living systems. The study of organic chemistry has led to enormous benefits in practical terms, such as in the production of textiles, paints, plastics, fuels, and pharmaceuticals.
It was once thought that certain compounds, called "organic compounds," were produced only by living organisms. The study of such compounds was therefore called organic chemistry. However, the defining notion of organic compounds was proven false in 1828, when Friedrich Woehler accidentally synthesized the biologically significant compound urea by evaporating an aqueous solution of ammonium cyanate (NH4OCN). Later, the term "organic chemistry" was redefined to mean the chemistry of the compounds of carbon.
Organic compounds are covalently bonded and thus, its bonds are directional. This allows for unique structures such as long carbon chains and rings. The reason carbon is excellent at forming unique structures and that there are so many carbon compounds is that carbon atoms form very stable covalent bonds with one another (catenation). In contrast to inorganic materials, organic compounds typically melt, sublime, or decompose below 300°C. Neutral organic compounds tend to be less soluble in water compared to many inorganic salts, with the exception of certain compounds such as ionic organic compounds and low molecular weight alcohols and carboxylic acids where there is hydrogen bonding present. Organic compounds tend to be much more soluble in organic solvents such as ether or alcohol, but the solubility in each solute is dependent on the functional groups present and of the general structure.
Organic nomenclature is the system established for naming and grouping organic compounds.
Aliphatic compounds are organic molecules that do not contain aromatic systems. Typically, they contain hydrocarbon chains.
Aromatic compounds are organic molecules that contain one or more aromatic ring system. This usually means, but is not limited to, those compounds that contain a benzene ring.
Heterocyclic compounds are cyclic organic molecules whose ring(s) contain at least one heteroatom. These heteroatoms can include oxygen, nitrogen, phosphorus, and sulfur.
These are parts of an organic molecule characterized by a specific composition and connected structure of the constituent atoms. Each functional group has a specific pattern of properties and reactions that characterize the compound. Some common functional groups are: Alcohols, Aldehydes, Amides, Amines, Carboxylic acids, Esters, Ethers, Ketones, Nitriles.
Polymers form a special group of molecule. Generally considered "large" molecules, polymers get their reputation regarding size because they are molecules that consist of multiple smaller segments. The segments could be chemically identical, which would make such a molecule a homopolymer. Or the segments could vary in chemical structure, which would make that molecule a heteropolymer. Polymers are a subset of "macromolecules" which is just a classification for all molecules that are considered large.
Polymers can be organic or inorganic. Commonly encountered polymers are usually organic (such as polyethylene, polypropylene, or Plexiglass). But inorganic polymers (such as silicone) are also part of familiar items.
Currently, there exist several methods for characterizing an organic compound. In general usage is (in alphabetical order):
Due to the huge number of possible organic compounds, an important part of organic chemistry is understanding the synthesis and reactions of organic compounds. There are distinct patterns based on functional group and carbon structure that can be applied to classes of compounds, see organic reaction. Many types of reaction bear the name of the person who discovered it, such as Grignard reactions, or the Williamson synthesis of ethers. Modern organic chemistry also tries to understand the mechanism, or process at the molecular level, for each type of reaction.
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