Chemical Formulae

Chemical Formulae
When the chemical composition of an official substance is known or generally accepted, the graphic and molecular formulae, the molecular weight and the Chemical Abstracts Service Registry Number are normally given at the beginning of the monograph for information. This information refers to the chemically pure substance and is not to be regarded as an indication of the purity of the official material. Elsewhere, in statements of standards of purity and strength and in descriptions of processes of assay, it is evident from the context that the formulae denote the chemically pure substances.
Where the absolute stereochemical configuration is specified, the International Union of Pure and Applied Chemistry (IUPAC) R/S and E/Z systems of designation have been used. If the substance is an enantiomer of unknown absolute stereochemistry the sign of the optical rotation, as determined in the solvent and under the conditions specified in the monograph, has been attached to the systematic name. An indication of sign of rotation has also been given where this is incorporated in a trivial name that appears on an IUPAC preferred list.
All amino acids, except glycine, have the L-configuration unless otherwise indicated. The three-letter and one-letter symbols used for amino acids in peptide and protein sequences are those recommended by the Joint Commission on Biochemical Nomenclature of the International Union of Pure and Applied Chemistry and the International Union of Biochemistry.
In the graphic formulae the following abbreviations are used:
Me –CH3 Bus–CH(CH3)CH2CH3
Et –CH2CH3 Bun–CH2CH2CH2CH3
Pri –CH(CH3)2 But–C(CH3)3
Prn –CH2CH2CH3 Ph–C6H5
Bui –CH2CH(CH3)2 Ac–COCH3