Naslov
Nucleofugality of Phenyl and Methyl Carbonates

Autori
Denegri, Bernard ; Kronja, Olga

Izvornik
Journal of Organic Chemistry (0022-3263) 72 (2007), 22; 8427-8433

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
nucleofugality

Sažetak
A series of X, Y-substituted benzhydryl phenyl carbonates 1 and X, Y-substituted benzhydryl methyl carbonates 2 were subjected to solvolysis in different methanol/water, ethanol/water, and acetone/water mixtures at 25 C. The LFER equation, log k = sf(Ef + Nf), was used to derive the nucleofuge-specific parameters (Nf and sf) for phenyl carbonate (1LG) and methyl carbonate (2LG) leaving groups in a given solvent in SN1 type reaction. Kinetic measurements showed that phenyl carbonates solvolyze one order of magnitude faster than methyl carbonates. Optimized geometries of 1LG and 2LG at B3LYP/6-311G(d, p), B3LYP/6-311++G(d, p), and MP2(full)/6-311++G(d, p) levels revealed that negative charge delocalization in carbonate anions to all three oxygen atoms occurs due to negative hyperconjugation. Phenyl carbonate (1LG) is a better leaving group (Nf = -0.84 ± 0.07 in 80% v/v aq EtOH) than methyl carbonate 2LG (Nf = -1.84 ± 0.07 in 80% v/v aq EtOH) because of more pronounced negative hyperconjugation, which is characterized with a more elongated RO-C bond and more increased RO-C-CO angle in 1LG than in 2LG. Calculated affinities of benzhydryl cation toward methyl and phenyl carbonate anions (Eaff = 11.7 kcal/mol at the B3LYP/6-311++G(d, p) level and Eaff = 2.7 kcal/mol at the PCM-B3LYP/6-311++G(d, p) level in methanol, respectively) showed that 1LG is more stabilized than 2LG, which is in accordance with greater solvolytic reactivity of 1 than 2.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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