Rates of Solvolysis of the Halophenyldimethylcarbinyl Chlorides. The Effect of Halogen Substituents upon the Rates of Electrophilic Reactions^1-3

Abstract

The twelve o-, m-and ^-monohalophenyldimethylcarbinyl chlorides were synthesized and their rates of solvolysis in 90% aqueous acetone (by volume) determined at several temperatures. Within each of the three isomeric series, the observed order of reactivity is F > Cl > Br < I. The observed magnitudes of the rate constants together with the observed reactivity orders can be rationalized in terms of the inductive effect, resonance and steric inhibition of resonance.Thus in the meta series it appears that the inductive effect is dominant, with a minor resonance contribution which increases the electron density at the ortho positions, whence it is relayed to the electron deficient reaction center by induction.In the para position, both induction and resonance appear to be of nearly equal (but opposite) effect. The lower rates exhibited by the ortho halogen substituents are attributed to an increased inductive effect and a reduced resonance effect, the latter arising from a partial resonance inhibition due to the conflicting steric requirements of the ortho substituents and the coplanar dimethylcarbinyl group of the incipient carbonium ions.

Solvolysis of 2‐chloro‐2(3,4‐disubstituted) phenylpropanes: Validity of Hammett–Brown σ+ constants in assessing additive effects of substituents

“… Plot of log k XY / k HH rate constants for the solvolysis in 90% aqueous acetone at 298 K of 2‐chloro‐2(3‐halo‐4‐methyl)phenylpropanes ( 3b–3d ), 2‐chloro‐2(3‐methoxy‐4‐methyl) phenylpropane ( 3e ), and 2‐chloro‐2(3‐methyl‐4‐methyl)phenyl propane ( 3f ) against Σσ + constants 32. In the figure, letters in superscripts indicate references: a 34, b 25, c 30, d 31, and e 9. *For monosubstituents, X = H, Y = 3‐F,3‐Me or 3‐MeO, and Σσ + = 0 + σ + for Ysubstituent.…”

“…Solvolysis rate . Following the procedure by Brown et al 31, the specific rates of solvolysis of the disubstituted chlorides R 1 R 2 ‐C 6 H 4 ·CMe 2 Cl were measured in 90% aqueous acetone at 288, 298, and 308 K, and the values are given in Tables II and III. These measured rate constants gave excellent first‐order behavior, as shown by the constancy of the rate coefficient throughout the course of a single run.…”

Cyclic Haloiodanes: Syntheses, Applications and Fundamental Studies

“…Martin and Amey have studied the reaction rates of photoinitiated halogenation of substituted tolyl derivatives by different reagents [113] . They found a good linear relationship between the logarithm of the reaction constants and Brown ’s σ + values [114–117] (analogous to Hammett ’s σ values) of the substrate's substituents.…”

Palladium- and Nickel-Catalyzed Cross-Couplings of Unsaturated Halides Bearing Relatively Acidic Protons with Organozinc Reagents

“…Purification of the crude residue obtained after evaporation of the solvents by flash chromatography (pentane/ether 7:3) yields 2-methyl-3'-trifluoromethyl-biphenyl-4-ylamine (3l) as a colorless oil (698 mg, 93%). (28), 165 (22), 152 (11), 90 (20).…”

“…(EI, 70 eV), m/z (%): 411(5) [M + ], 396(9), 380 (100), 294(21), 204(11).IR (cm -1 ): 3460 (m), 3331 (m), 3027 (w), 2869 (m), 2928 (m), 2953 (m), 1666 (vs), 1601 (m), 1582 (m), 1510 (w), 1483 (m), 1452 (m), 1435 (m), 1403 (m), 1367 (m), 1274 (s), 1232 (schloride (1l, 2.2 mL, 1.08 M in THF, 2.4 mmol, prepared by the direct zinc insertion into the benzylic chloride 4 ) is added to a solution of 2-(5-bromo-1H-indol-3-yl)-2-phenyl-ethanol (8j, 632 mg, 2 mmol), Pd(OAc) 2 (4.5 mg, 0.02 mmol), S-Phos (L3, 16.4 mg, 0.04 mmol) in THF (2 mL), according to TP 2. The reaction mixture was stirred for 1 h at 25 °C.…”