Nucleophilic Substitution Post Lab Quiz Study Guide

Nucleophilic Aliphatic Substitution

A reaction in which a nucleophile replaces a leaving group attached to an sp3-hybridized carbon atom.

SN1

A unimolecular, two-step substitution mechanism in which the leaving group first dissociates to form a carbocation, followed by nucleophilic attack.

SN2

A bimolecular, one-step substitution mechanism in which the nucleophile attacks from the backside as the leaving group leaves, causing inversion of stereochemistry.

Infrared Spectroscopy (IR)

A technique used to identify functional groups by measuring the absorption of infrared light at different frequencies.

Halide Test

A qualitative test used to identify and distinguish alkyl halides and determine their reactivity through precipitation reactions.

Nucleophilic Substitution Requirements

A substitution reaction requires a leaving group, a nucleophile, and a suitable substrate.

Leaving Group

A group that leaves the molecule with the bonding electron pair. Good leaving groups are stable after leaving.

Nucleophile

A negatively charged or neutral species with a lone pair of electrons that attacks an electrophilic carbon.

Why Did We Choose HCl?

HCl protonates the alcohol's OH group, turning it into water, a good leaving group. It also provides chloride ions to form the product.

SN1 vs. SN2

SN1 occurs in two steps through a carbocation intermediate and favors tertiary substrates. SN2 occurs in one step through backside attack and favors primary substrates.

Wash vs. Extraction

Extraction separates compounds based on solubility in two immiscible liquids. Washing removes unwanted impurities from a desired layer.

General Reaction and Mechanism

2-methyl-2-butanol reacts with HCl. The OH group is protonated, water leaves to form a tertiary carbocation, and chloride attacks to produce 2-chloro-2-methylbutane.

IR Analysis

IR spectroscopy identifies functional groups by measuring the absorption of infrared radiation by chemical bonds.

Three Functional Group Frequencies

O-H: 3200–3600 cm⁻¹; C-H: 2850–3100 cm⁻¹; C-Cl: 600–800 cm⁻¹.

Peak Intensity vs. Peak Frequency

Intensity indicates how strongly a bond absorbs IR radiation. Frequency indicates the vibrational energy and helps identify the bond.

Percent Yield Analysis

Percent yield compares the actual amount of product obtained to the theoretical amount possible.

Percent Yield Formula

Percent yield = (actual yield ÷ theoretical yield) × 100.

Halide Test Analysis

Silver nitrate tests SN1 reactivity, while sodium iodide tests SN2 reactivity. Precipitate formation indicates a reaction occurred.