Degenerate rearrangement of 9-isopropenyl-9,10-dimethyl-phenanthren-9-yl and 9,10-dimethyl-9-(trans-1-methylprop-1-en-1-yl)phenanthren-9-yl cations

Long-lived cationic complexes: “frozen” intermediates of cationoid reactions

“…A very sharp (by five orders of magnitude) slowing down of the degenerate rearrangement going from cation 1c to 1d, 28,29 i.e., when the cis dimethylvinyl migrant was replaced by the trans dimethylvinyl one, turned out to be quite unexpected. Geometric characteristics of the initial and transition states of the rearrangements have been obtained 29 by the DFT method ("PRIRODA" program 34, 35 ).…”

Relative stability of isomeric carbocations with migrating groups in the neighboring positions

“…As shown in [11], the rate of degenerate rearrangements of cations β-I via 1,2-shift of methyl-substituted vinyl groups is largely determined by steric factors. These factors are also significant for cations α-I.…”

“…When R = H [6], Et [2], ClCH 2 [7], Cl 2 CH [5], CH 2 =C(Me) [11], Ph, p-MeC 6 H 4 , p-FC 6 H 4 , m-FC 6 H 4 , p-F 3 CC 6 H 4 , C 6 F 5 [3], O 2 N [7], the equilibrium is displaced toward β-isomer, whereas α-and β-isomeric carbocations with R = p-MeOC 6 H 4 [3], CH 2 =CH [10], trans-MeCH=C(Me) [11], cyclopropyl [12], and Cl [4] are characterized by comparable stabilities. Therefore, for most of the above listed migrating groups we succeeded in determining by dynamic NMR the rate of 1,2-shift, not being concerned about almost complete transformation of β-isomer I into α-isomer as a result of 1,2-shift of methyl group.…”

“…Dihedral angle C 8a C 9 C 10 C 10a in cations α-I, deg [12] 0, 34 b 0-3.0--24.6-CH 2 =CH [10] 16 0-9.1--24.0-CH 2 =C(Me) [11] 17 09.0 -16.1-cis-MeCH=C(Me) [9] 29 0-5.6--39.5-trans-MeCH=C(Me) [11] 22 0-6.5--35.3-Ph [3] 25 00.4 -22.5-p-MeC 6 H 4 [3] 26 00-6.02--30.4-p-MeOC 6 H 4 [3] 26 -17. grating groups R is determined by specific steric requirements of the phenanthrene skeleton (cf. [3]).…”

“…Long-lived 9-R-9,10-dimethylphenanthrenyl cations are capable of undergoing degenerate rearrangement via 1,2-shift of the R substituent (Scheme 1) and are therefore convenient models for studying relative migration abilities of various atoms and groups [2][3][4][5][6][7][8][9][10][11][12].…”