A theoretical approach to the Birch reduction. Structures and stabilities of cyclohexadienes

Ab initio study of 3‐furyl fulgide I. Molecular structures and relative stabilities of three isomers

“…It is apparent from Table 1 that the bond formation of C12-C10-C8-C1-C2-C9 changes from the single bond to the double bond and from double to single by the ring-closure reaction from the E-isomer. The bond distance C9-C12 is 1.571Å, being longer than the 1.549Ådetermined by the STO-3G basis set [17] and the experimental value of 1.534Å [18] of 1,3-cyclohexatriene. However, the bond angles C19-C9-C2, C18-C9-C2 and C15-C12-C10 around the atoms corresponding to the bond formation in ring-closure reaction are 109.0, 119.7 and 108.3 • , respectively, showing that a strain-free bond is formed in the C-isomer.…”

Birch Reduction of Benzene in a Low‐Temperature Plasma

“…It is likely that some 1,3cyclohexadiene is formed from 1,4-cyclohexadiene as a result of isomerization promoted by its greater stability. [16] The Figure 3. LTP mass spectra of benzene with: A) a discharge chamber containing a silicon wafer surface exposed to the plasma, and B) a discharge chamber containing an SiÀH-modified silicon wafer exposed to the plasma.…”

“…further reduction of 1,4-cyclohexadiene is not favorable because of its low reactivity toward electron addition, [16,17] which results in dihydrogenation being the main reduction pathway. Efforts have been made to identify the proposed reaction intermediates-including benzene radical anions, cyclohexadienyl radicals, and cyclohexadienyl anions.…”

ipso Nitration. XXVIII. Nitration of 4-substituted toluenes: 1,2 adducts

“…Ab initio molecular orbital calculations carried out by Birch et al indicate that the 4-substituted 1,2-dihydrobenzene is of lower energy than the 4-substituted 1,4-dihydrobenzene over a range of substituents (32). This supports the conclusion that adduct formation is subject to kinetic control since under equilibrium conditions the 1 , 2 adduct should be favoured for all substituents.…”