Question

Introduction Alkyl halides can be prepared from alcohols by reactions with hydrogen halides (HCI, HBr, or HI) via nucleophilic substitution. In this type of reaction, the nucleophile displaces a leaving group from a carbon atom of an organic substrate (here the alcohol once protonated). Both electrons of the new bond to the carbon are provided by the nucleophile while the leaving group departs with both electrons of its bond to the substrate. There are two limiting mechanisms that are most common in describing nucleophilic substitution reactions at sp carbon centres : (1) a direct displacement (SN2) process and (2) a process that generates an intermediate carbocation (SN1). Which mechanism is a better description depends on the structure of the molecule containing the leaving group, the nature of the leaving group, the size of the nucleophile, and the polarity of the solvent. This experiment is a near-perfect example of an Sn1 substitution. H3COH + HCI H3CCI + H2O (Equation 1) H3C CH3 H3C CH3 In this reaction, you will prepare 2-chloro-2-methylpropane (t-butyl chloride) from 2- methyl-2-propanol (t-butyl alcohol) using HCl as the strong acid and chloride source. Note that HCI first activates the alcohol in an acid/base reaction before the Sn1 reaction proceeds. The final product is characterized by its yield, boiling point, and density. The presence of a halide atom is confirmed with a silver nitrate test.

1) State which of the electrophiles given below will react preferentially by i) SN1, ii) by SN2, or iii) capable of reacting by either of the two mechanisms depending on the given conditions. How can you affect those conditions to favour SN1 or SN2? Reason your predictions based on the structures of the compounds. Br-CH3, Br-CH2CH3, Br-CH(CH3)2, Br-C(CH3)3, Br-CH2-C5H6; C5H6 = phenyl

Answer 1

Br-CH3 (halibl SN2 ype r-cH, (alry SN2 yb(steaky holids Lus hunduud So diet attauk) CCHC -B (2alkyl halioke) Capable of Luaetny by eithr o tho two dibend on the noiuent ohich wed fom eautton Polar Pole sbluentsSN. Potar aproiee solverts N 6T-CCCH)33alyi halrdl move Atable caubocotion SNI Bi-CH-CS 16 (SN2 alkylhalis