“…Electronic interactions at the R-O-C]O groups in carbamates and esters are less understood than that at the R-N-C]O groups in amides. Carbamates in which both these groups are fused at the carbonyl C]O bond, have several ester-like rather than amide-like features 1,2 including comparable C-O bond lengths in crystals, [3][4][5][6] favourable interactions between the dipoles of the C]O and O-R bonds in the predominant s-trans rotamers of the R-O-C]O groups and unfavourable lone pair repulsion between the two ester oxygens in their trace s-cis rotamers [7][8][9][10] (Fig. 1a).…”
mentioning
confidence: 99%
“…Fig.2 (a and b) Incremental downfield shifts in the13 C and 1 H signals of H a and C a in carbamates (1-8) and esters(9)(10)(11)(12)(13)(14)(15)(16) relative to the corresponding homologous alcohols (17-20), indicating the stabilization of positive charge polarization at C a by hyperconjugative resonance from the C b H 3 groups; (c and d) inverse correlation between 13 C and 1 H NMR signals of C a and H a and FT-IR stretching frequencies at C]O in carbamates (1-7) and esters (9-15) with increasing number of methyl (C b H 3 ) substituents (0-2) on C a (for isopropyl N-phenyl carbamate (7), the FT-IR value is not inserted); (e) upfield shifts in the C b signals of carbamates (1-8) and esters (9-16) compared to corresponding alcohols (17-20), indicating electronic back donation towards C b ; (f) shifts in the H b signals of carbamates (1-8) and esters (9-16) compared to corresponding alcohols (17-20), indicating the dominance of charge / HCR* interactions. The lines merely indicate the trends.…”
NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.
“…Electronic interactions at the R-O-C]O groups in carbamates and esters are less understood than that at the R-N-C]O groups in amides. Carbamates in which both these groups are fused at the carbonyl C]O bond, have several ester-like rather than amide-like features 1,2 including comparable C-O bond lengths in crystals, [3][4][5][6] favourable interactions between the dipoles of the C]O and O-R bonds in the predominant s-trans rotamers of the R-O-C]O groups and unfavourable lone pair repulsion between the two ester oxygens in their trace s-cis rotamers [7][8][9][10] (Fig. 1a).…”
mentioning
confidence: 99%
“…Fig.2 (a and b) Incremental downfield shifts in the13 C and 1 H signals of H a and C a in carbamates (1-8) and esters(9)(10)(11)(12)(13)(14)(15)(16) relative to the corresponding homologous alcohols (17-20), indicating the stabilization of positive charge polarization at C a by hyperconjugative resonance from the C b H 3 groups; (c and d) inverse correlation between 13 C and 1 H NMR signals of C a and H a and FT-IR stretching frequencies at C]O in carbamates (1-7) and esters (9-15) with increasing number of methyl (C b H 3 ) substituents (0-2) on C a (for isopropyl N-phenyl carbamate (7), the FT-IR value is not inserted); (e) upfield shifts in the C b signals of carbamates (1-8) and esters (9-16) compared to corresponding alcohols (17-20), indicating electronic back donation towards C b ; (f) shifts in the H b signals of carbamates (1-8) and esters (9-16) compared to corresponding alcohols (17-20), indicating the dominance of charge / HCR* interactions. The lines merely indicate the trends.…”
NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.