Aromatic in the context of "Amino acids"

Pyrimidine (C₄H₄N₂; /pɪˈrɪ.mɪˌdiːn, paɪˈrɪ.mɪˌdiːn/) is an aromatic, heterocyclic, organic compound similar to pyridine (C₅H₅N). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other diazines are pyrazine (nitrogen atoms at the 1 and 4 positions) and pyridazine (nitrogen atoms at the 1 and 2 positions).

In nucleic acids, three types of nucleobases are pyrimidine derivatives: cytosine (C), thymine (T), and uracil (U).

Purine is a heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines and their tautomers. They are the most widely occurring nitrogen-containing heterocycles in nature.

Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life.

Amino acids can be classified according to the locations of the core structural functional groups (alpha- (α-), beta- (β-), gamma- (γ-) amino acids, etc.); other categories relate to polarity, ionization, and side-chain group type (aliphatic, acyclic, aromatic, polar, etc.). In the form of proteins, amino-acid residues form the second-largest component (water being the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis. It is thought that they played a key role in enabling life on Earth and its emergence.

Cresols (also known as hydroxytoluene, toluenol, benzol or cresylic acid) are a group of aromatic organic compounds. They are widely-occurring phenols (sometimes called phenolics) which may be either natural or manufactured. They are also categorized as methyl phenols. Cresols commonly occur as either solids or liquids because their melting points are generally close to room temperature. Like other types of phenols, they are slowly oxidized by exposure to air, and the resulting impurities often give the samples a yellow to brownish red tint. Cresols have an odor characteristic to that of other simple phenols, reminiscent to some of a "coal tar" smell. The name "cresol" is an adduct of phenol and their traditional source, creosote.

A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions are of prime importance in organic chemistry. Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to predict the product outcome in a reaction. It also is helpful for optimizing a reaction with regard to variables such as temperature and choice of solvent.

A good example of a substitution reaction is halogenation. When chlorine gas (Cl₂) is irradiated, some of the molecules are split into two chlorine radicals (Cl•), whose free electrons are strongly nucleophilic. One of them breaks a C–H covalent bond in CH₄ and grabs the hydrogen atom to form the electrically neutral HCl. The other radical reforms a covalent bond with the CH₃• to form CH₃Cl (methyl chloride).

Hexacene is an aromatic compound consisting of six linearly-fused benzene rings. It is a blue-green, air-stable solid with low solubility.

Hexacene is one of a series of linear polycyclic molecules created by such aromatic ring fusions, a series termed acenes; the previous in the series is pentacene (with five fused rings) and the next is heptacene (with seven). It and other acenes and their derivatives have been investigated in potential applications related to organic semiconductors. Like larger acenes, hexacene is poorly soluble, but derivatives have been prepared with improved solubility, such as 6,15-Bis(tri-t-butylsilylethynyl)hexacene, which melts with decomposition at 96 °C.

A bicyclic molecule (from bi 'two' and cycle 'ring') is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring atoms are carbons), or heterocyclic (the rings' atoms consist of at least two elements), like DABCO. Moreover, the two rings can both be aliphatic (e.g. decalin and norbornane), or can be aromatic (e.g. naphthalene), or a combination of aliphatic and aromatic (e.g. tetralin).

Three modes of ring junction are possible for a bicyclic compound:

Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C₄H₄N₂. It is a symmetrical molecule with point group D_2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a "deliquescent crystal or wax-like solid with a pungent, sweet, corn-like, nutty odour".

Pyrazine and a variety of alkylpyrazines are flavor and aroma compounds found in baked and roasted goods. Tetramethylpyrazine (also known as ligustrazine) is reported to scavenge superoxide anions and decrease nitric oxide production in human granulocytes.

Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula C₄H₄N₂. It contains a six-membered ring with two adjacent nitrogen atoms. It is a colorless liquid with a boiling point of 208 °C. It is isomeric with two other diazine (C₄H₄N₂) rings, pyrimidine and pyrazine.