Catalysis by hydrogen halides in the gas phase. Part XII. Trimethylacetic acid and hydrogen bromide

Charge-transfer transitions of 2:1 electron donor-acceptor complexes

“…)-1/2 (-1)'>µ,(1) 1(2) 2(3) 2(4)... («-1)0 ( ) (3) p where , 2,... are the occupied molecular orbitals of the donor and acceptor molecules in their ground-state configurations, and 0 is the donor HOMO. The wave function of the ionic state is expressed as the linear combination of two Slater determinants ^,(D+A~) = [2(1 + 5 2)]-2 -) (4) where the minus sign is chosen to describe the singlet excited state, (5) The Slater determinants which contribute to the ionic wave function differ from 0 in the promotion of an electron from the donor HOMO </>D to the acceptor LUMO . With the assumption that the only nonzero overlap between molecular orbitals on different molecules is that of the donor HOMO with the acceptor LUMO, Mulliken derived the following expression for the transition dipole moment Mge = a*b(ui -Mo) + (m*mb*b)eS(rD -rDA) (7) where µ and µ0 are the dipole moments of the ionic and no-bond states, respectively, e is the charge on the electron, and the other quantities are S = ( 0\ ) = (2)V2Sda/(1 + Sda2)1/2 (8) •Sda = ( \ ) (9) 'd = (</>dI'|0d) (10) 'da = (^dI'I^aI/^da (11) Mulliken estimated the quantities rDA and µ, as follows:…”

“…If we neglect a difference in solvent effects, eq 16 would predict a red shift of the CT spectrum upon addition of the second donor, since mixing the no-bond wave function into the ionic wave function destabilizes the excited state. 4 In fact, the CT spectrum of the 2:1 complex of HMB with TCNE is slightly red-shifted (200-300 cm"1) with respect to that of the 1:1 complex.1,3 The small value of this shift also implies that the resonance integral connecting the left and right ionic states is small: Hrl = (^(D+A"D)Wr(DA"D+)> (17) HRL is expected to be small because of the weak interaction of HOMO's localized on different donors. Thus the energy of the symmetric excited state fs = 1/21/2[^l(D+A"D) + V-r(DA"D+)] ( 18) is close to that of the antisymmetric excited state.…”

Reactions of methyl benzoate and methyl formate with hydrogen bromide and hydrogen iodide

“…Department of Chemistry, University of Calgary, Calgary, Alberta, Canada (Received May 6,1970) The decomposition of 1,1-difluoroethylene has been studied in a single-pulse shock tube over the temperature range of 1290 to 1700°K at total reflected shock pressures of about 3 to 4 kTorr and reaction dwell times of about 10""8 sec. At low conversions, below 1480°K , the principal reaction is the unimolecular elimination of HF with the first-order rate constant given by h = 14'4*1'1 exp[-(86,000 ± 6800)/ñZ] sec-1.…”