定义Definition
氨基是 –NH₂ 基团，是伯胺的官能团，也存在于氨基酸中。氮原子上的孤电子对能接受质子，使含氨基的化合物呈碱性：RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻。广义上 –NHR、–NR₂ 也称取代氨基。
The amino group, –NH₂, is the functional group of primary amines and is also found in amino acids. The lone pair on nitrogen accepts a proton, making compounds with an amino group basic: RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻. –NHR and –NR₂ are called substituted amino groups.
碱性的比较Comparing basicity
烷基的给电子诱导效应使氮上电子密度增大，所以乙胺的碱性强于氨；苯胺中氮的孤电子对与苯环共轭离域，碱性弱于氨；酰胺中的氮几乎没有碱性。
The electron-donating inductive effect of alkyl groups raises the electron density on nitrogen, so ethylamine is a stronger base than ammonia; in phenylamine the lone pair is delocalised into the ring, making it a weaker base than ammonia; the nitrogen of an amide is hardly basic at all.
在氨基酸中In amino acids
α-氨基酸同时含氨基和羧基，在水溶液中主要以两性离子 ⁺H₃N–CHR–COO⁻ 形式存在。氨基与另一分子的羧基缩合形成肽键。
α-Amino acids contain both an amino and a carboxyl group and exist in water mainly as zwitterions, ⁺H₃N–CHR–COO⁻. The amino group condenses with the carboxyl group of another molecule to form a peptide bond.