MBB 222 Lecture Notes - Lecture 3: Aromatic Amino Acids, Phenylalanine, Aliphatic Compound
30 Mar 2018
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The (cid:373)ole(cid:272)ules (cid:271)elo(cid:449) ha(cid:448)e dis(cid:272)(cid:396)ete si(cid:374)gle a(cid:374)d dou(cid:271)le (cid:271)o(cid:374)ds: thei(cid:396) ele(cid:272)t(cid:396)o(cid:374)s a(cid:396)e (cid:862)lo(cid:272)alized(cid:863) about the individual bonds and atoms. The molecule below does not have discrete single and double c-o bonds the electron pairs circulate across the o-c-o atoms the(cid:455) a(cid:396)e (cid:862)delo(cid:272)alized(cid:863). The delo(cid:272)alizatio(cid:374) of ele(cid:272)t(cid:396)o(cid:374)s a(cid:272)(cid:396)oss (cid:271)o(cid:374)ds is (cid:272)alled (cid:396)eso(cid:374)a(cid:374)(cid:272)e. neithe(cid:396) of the (cid:862)(cid:396)eso(cid:374)a(cid:374)(cid:272)e (cid:272)o(cid:374)t(cid:396)i(cid:271)uto(cid:396)s(cid:863) sho(cid:449)(cid:374) o(cid:374) the left a(cid:272)(cid:272)u(cid:396)atel(cid:455) depi(cid:272)ts the t(cid:396)ue e- distribution as they are not in e(cid:395)uili(cid:271)(cid:396)iu(cid:373) (cid:894)(cid:374)ot (cid:272)ha(cid:374)gi(cid:374)g f(cid:396)o(cid:373) o(cid:374)e to the othe(cid:396)(cid:895). The a(cid:272)tual st(cid:396)u(cid:272)tu(cid:396)e is the (cid:862)(cid:396)eso(cid:374)a(cid:374)(cid:272)e h(cid:455)(cid:271)(cid:396)id. (cid:863) delo(cid:272)alizatio(cid:374) of e- results in a more stable molecule. Pi electrons and lone pair electrons can be moved to an sp2 carbon. A(cid:373)i(cid:374)o a(cid:272)ids a(cid:396)e li(cid:374)ked i(cid:374) peptides/p(cid:396)otei(cid:374)s (cid:271)(cid:455) a (cid:272)o(cid:448)ale(cid:374)t (cid:862)peptide (cid:271)o(cid:374)d(cid:863). Delo(cid:272)alizatio(cid:374) of the electrons imposes partial double bond character on the bonds and limits rotation about those bonds. This limited rotation about the peptide bond (see red arrows) influences the folding of that polypeptide.
