a2aoa mage and Mirrer lege af N-Meths CHAL nema 70 because mrve =●R s form weaker hydrogen bonds than alcohol ie bet those of the -o3 Smaller amines are soluble in water (hydrogen bonding). iehehrehapetofanamineexceedssacarborns,the aa le in water 21-3 Spectroscopy of the Amine Group ear 1600 cm-',due to a these signals since they do 22 When an amine bears three different substituents (plus the lone pair of electrons), it has the potential to be optically active: At ordinary temperatures amines are not optically active, however because of a rapid isomerization process called inversion. The transition state for the inversion of an amine has been found to be between 5 and 7 kcal mol-1 for ordinary small amines. It is therefore impossible to keep an enantiomerically pure, simple di- or trialkylamine from racemizing at room temperature when the nitrogen atom is the only stereocenter. Amines form weaker hydrogen bonds than alcohols do. As a result, their boiling points are lower and their solubilities in water are lower. The boiling points of amines generally lie between those of the corresponding alkane and alcohol. Smaller amines are soluble in water (hydrogen bonding). When the hydrophobic part of an amine exceeds six carbons, the solubility in water decreases rapidly. Larger amines are essentially insoluble in water. 21-3 Spectroscopy of the Amine Group Primary and secondary amines exhibit a characteristically broad IR N-H stretching absorption between 3250 and 3500 cm-1. Primary amines show two strong peaks in this range, whereas secondary amines show only one. Primary amines also show a band near 1600 cm-1, due to a scissoring motion of the NH2 group. Tertiary amines do not show any of these signals since they do not have a hydrogen bound to nitrogen. The NMR spectra of amines often give broadened peaks similar to the OH signal in alcohols. The chemical shifts depend upon the exchange rate of protons with water in the solvent and the amount of hydrogen bonding. The lowest field hydrogens are those neighboring the nitrogen atom and are deshielded due to the nitrogen’s electronegativity