Amide—A functional group containing a carbonyl and an amino group (RCONR 2 ).
Amino acids—Dipolar compounds that contain an amine and a carboxylic acid attached to a single
carbon (the α-carbon); the building blocks of peptides.
Amphoteric—Describes molecules that can act as both acids and bases.
Angle strain—Increased energy that results when bond angles deviate from their ideal values.
Anhydride—A functional group containing two carbonyls separated by an oxygen atom (RCOOCOR);
often the condensation dimer of a carboxylic acid.
Anti conformation—A type of staggered conformation in which the two largest groups are
antiperiplanar to each other; the most energetically favorable conformation.
Antibonding orbital—A higher-energy, less stable orbital that results from the overlap of wave
functions with opposite signs.
Antiperiplanar—A conformation in which substituents are in the same plane, but on opposite sides
of a bond.
Axial—Describes groups on a cyclic molecule that are perpendicular to the plane of the molecule,
pointing straight up or down.
Azimuthal quantum number (l)—Describes the subshell in which an electron is found; possible
values range from 0 to n − 1, with l = 0 representing the s subshell, l = 1 representing p, l = 2
representing d, and l = 3 representing f.
β-lactam—Four-membered cyclic amides that are more reactive to hydrolysis than linear amides or
larger cyclic amides; often used as the backbone for antibiotics.
β-state—A magnetic state seen in NMR spectroscopy in which nuclei have been irradiated with
radiofrequency pulses to bring them to a higher-energy state.
Bonding orbital—A lower-energy, more stable orbital that results from the overlap of wave
functions with the same sign.