RELATIVE IMPORTANCE OF STERIC AND INDUCTIVE EFFECTS IN S_N2 DISPLACEMENT REACTIONS

Abstract

Table I Exchange Reactions Catalyzed by the P Enzyme In experiment A, the complete system contained 1.3 µ . succinyl CoA, 50 µ . TRIS pH 7.4, 5 µ . C14-succinate, 0.17 mg. enzyme protein (5.2 units), 5µ . P04 and 5µ . MgClj; 2.5 µ . ADP added when indicated; final volume 1.0 ml.; incubated 6 minutes at 20°. After incubation, NH2OH was added and the succinohydroxamic acid separated from succinate by chromatography on Dowex 1. About 0.90-1.17 µ .of succinohydroxamic acid was isolated from the column.

Solvolytic Displacement Reactions At Saturated Carbon Atoms

“…The rate measurements of Acree and Shadinger (2) did not give good second-order rate constants for the reaction of tert-butyl iodide with the sodium salt of l-phenyl-3-thiourazole (X) in 50 per cent aqueous alcohol; this reaction was doubtless complicated by concurrent solvolysis. Conant and Hussey (157) found that tert-butyl chloride is more reactive than isopropyl chloride towards potassium iodide in acetone, but this result is contradicted by more recent work (440,521).…”

“…On the other hand, the explanation has been offered that the greater effective bulk of increasing alkyl substitution sterically opposes the close approach of a nucleophilic reagent. This explanation is based on steric hindrance (115,233,235,380,449,521). The suggestion has also been made that the two effects are of comparable importance (198,222).…”

Rearrangement of 1-aryl-2,2-dihalo-1-alkanones

“…The relative reactivities of phenacyl chloride, 2-chloropropiophenone and a-chloroisobutyrophenone varied from 1 over 0.006 to 0.000 003. 21 As a matter of fact, -bromopropiophenone (15; Ar = Ph, R = Me, X = Br)22 and -chloropropiophenone (15; Ar = Ph, R = Me, X = Cl)23 are known to react with sodium methoxide in methanol to give 1,1-dimethoxy-1 -phenyl-2-propanol (17; Ar = Ph, R' = R = Me). The formation of -hydroxy acetal 17 was explained by carbonyl attack, epoxide (16) production, and subsequent opening by the nucleophile (Scheme VI).…”

“…The 4:1 ratio of 2b to 3b obtained at 0 °C was drastically changed into a 1:1 ratio when the substrate was dropped into a refluxing solution of sodium methoxide in methanol. It is clear that the rate of the reaction is very fast at temperatures above room temperature, but the distribution of products is determined by the temperature influence on the chemical behavior of a-chloro-a-methoxy-a-phenyl ketone 21 (R = R' = Me, X = Cl, Rx = R^= R3 = H). At higher temperature, the competition between solvolysis of the latter a-chloro ether and nucleophilic attack at the carbonyl function and subsequent epoxide formation will be shifted to the solvolysis pathway because of the predictable, more important influence on the carbon-halogen bond breaking of the -chloro ether.…”

“…The -bromo--chloro derivative 9 was converted mainly into the intermediate -chloro ether 21 (R = R' = Me, X = Cl, Rx = R2 = R3 = H) and, therefore, its results were not very different from the , -dichloro analogue lb. The rearrangement of , -dibromopropiophenone (6, R = Me) is completely determined by the solvolytic behavior of -bromo ether 21 (R = R' = Me, X = Br, Rx = R2 = R3 = H), which to a minor extent led to the carbonyl addition pathway. This result supports our proposal that the formal substitution products 2 are not a result of a direct displacement reaction.…”