Richard N. McDonald

Electroreduction of diphenyldiazomethane in acetonitrile at a hanging mercury drop electrode

Abstract Cyclic voltammetric studies of the reduction of diphenyldiazomethane (Ph 2 CN 2 ) in CH 3 CN-Me 4 NPF 6 at a hanging mercury drop electrode have established that the halflife of Ph 2 CN 2 ⨪ is less than l ms at either 8°C or −37°C.

Generation and ion-molecule reactions of ethyl diazoacetate anion radical (EtO2CCHN2XXX)

Abstract Thermal electron attachment to EtO 2 CCHN 2 produced the parent anion radical EtO 2 CCHN 2 -( m/z 114). The ion-molecule reactions of m/z 114 with 30 neutral substrates were examined. Using the bracketing method, PA(EtO 2 CCHN 2 XXX ) = 355±4 kcal mol -1 was determined. The reaction of m/z 4 with CH 3 SH produced H 2 CS XXX , the product of β-elimination of H + 2 from the thiol. From a series of bracketing studies and determination of the equilibrium constant for the electron transfer (ET) process CH 3 C(O)C(O)CH 3 - +EtO 2 CCHN 2 = CH 3 C(O)C(O)CH 3 +EtO 2 CCHN 2 XXX EA(EtO 2 CCHN 2 ) = 19.7 kcal mol -1 was derived. Both associative and dissociative ET were observed in the reactions of m/z 114 with certain perhalomethanes (depending on their EA) as well as halogen-atom abstraction from BrCCl 3 . While no reaction was observed between m/z 114 with CH 3 CHO or (CH 3 ) 2 CO, m/z 114 reacted with certain other ketones and esters (CF 3 CO 2 R) mainly to yield enolate anions of the β-keto esters, EtO 2 CCHC(O - )R. These enolate anions are believed to be formed by nucleophilic addition of C α of m/z 114 to the carbonyl group of the neutral substrate followed by loss of N 2 and radical β-fragmentation.

Formation of a 1,3-azulenediacylium ion in SbF5–FSO3H–SO2

The stepwise production of 6-bromoazulene-1,3-diacylium ion is observed from the diconjugate acid of 6-bromoazulene-1,3-dicarboxylic acid or diester via the monoacylium ion–monocarboxy-conjugate acid in SbF5–FSO3H–SO2.

Ligand addition versus substitution in the slow reaction of 13CO with Mn(CO)−4 in a flowing afterglow apparatus

Abstract The gas-phase reactions of Mn(CO) − 4 with CO and 13 CO are reported. Only addition was observed with CO producing Mn(CO) − 5 ( k app = (2.5±0.2) × 10 −12 cm 3 molecule −1 s −1 ). Both addition ( k add = (3.2 ±0.4) × 10 −12 cm 3 molecule −1 s −1 ) and substitution ( k sub = (1.2 ± 0.4) × 10 −12 cm 3 molecule −1 s −1 ) product-forming channels were observed in the reaction with 13 CO. The average branching fractions for addition and thermoneutral substitution are 0.74 and 0.26 respectively. These branching fractions and the 70% collisional quenching efficiency of the excited addition intermediates [Mn( 13 CO)(CO) − 4 ] ★ with the helium buffer gas are essentially the same values as those previously obtained for the quenching/decomposition of [Fe( 13 CO)(CO) − 3 ] ★ . The ground electronic state of Mn(CO) − 4 is believed to be the triplet because the negative ion is isoelectronic with Fe(CO) 4 , a known ground state triplet complex. Thus, the slow rate of the Mn(CO) − 4 /CO reaction (reaction efficiency = 0.0036) is considered to be the result of the spin-forbidden curve crossing of the triplet Mn(CO) − 4 + CO inlet surface to the attractive singlet Mn(CO) − 4 + CO → singlet Mn(CO) − 5 product surface. Comparisons with the results from the fast spin-allowed addition/substitution reactions of Fe(CO) − 3 with 13 CO are given.