Alcohols and Alkyl Halides: Introduction to Reaction Mechanisms Chapter 5 Alcohols and Alkyl Halides: Introduction to Reaction Mechanisms Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Section 5.1 FUNCTIONAL GROUPS

Functional Groups-1 Alkanes are not generally considered to be functional groups (although C–H bonds can be reactive) The multiple bonds in alkenes and alkynes are considered functional groups The six-membered rings consisting of 𝑠𝑝 2 hybridized carbons in arenes are considered functional groups In this chapter, we will focus on alcohols (ROH) and alkyl halides (RX, X = F, Br, Cl, I)

Survey of Functional Groups

Survey of Functional Groups-1

Survey of Functional Groups-2

IUPAC NOMENCLATURE OF ALKYL HALIDES Section 5.2 IUPAC NOMENCLATURE OF ALKYL HALIDES

Two Types of Nomenclature There are two distinct types of nomenclature for alkyl halides: Functional class nomenclature: the alkyl group is treated as the “positive” portion of a halide salt

Two Types of Nomenclature-1 There are two distinct types of nomenclature for alkyl halides: Functional class nomenclature: the alkyl group is treated as the “positive” portion of a halide salt Substitutive nomenclature (preferred): the halogen is treated as a “halo-” substituent on an alkyl chain

IUPAC NOMENCLATURE OF ALCOHOLS Section 5.3 IUPAC NOMENCLATURE OF ALCOHOLS

Two Types of Nomenclature-2 The two types of nomenclature we saw for alkyl halides apply to alcohols as well: Functional class nomenclature: the alcohol is named as an “alkyl alcohol”; the alkyl group is treated as a substituent

Two Types of Nomenclature-3 The two types of nomenclature we saw for alkyl halides apply to alcohols as well: Functional class nomenclature: the alcohol is named as an “alkyl alcohol”; the alkyl group is treated as a substituent Substitutive nomenclature (preferred): the alcohol is named as an “alkanol,” with a number before “alkan” or “ol” to denote the position of the –OH group Either the “n-alkanol” or “alkan-n-ol” names are acceptable.

Substitutive Nomenclature When using the substitutive convention, it is important that the parent chain includes the –OH or –X substituent For the purposes of numbering, the –OH group takes precedence over halogen substituents and alkyl groups

CLASSES OF ALCOHOLS AND ALKYL HALIDES Section 5.4 CLASSES OF ALCOHOLS AND ALKYL HALIDES

Substitution pattern can profoundly affect the reactivity of a carbon! Alcohols, alkyl halides, and other organic compounds are often classified by substitution pattern The key question is: how many alkyl groups are attached directly to the carbon that bears the functional group? One alkyl group: primary (𝟏°) Two alkyl groups: secondary (𝟐°) Three alkyl groups: tertiary (𝟑°) Substitution pattern can profoundly affect the reactivity of a carbon! One attached alkyl group; Two implicit hydrogens Two attached alkyl groups; Two implicit hydrogens

BONDING IN ALCOHOLS AND ALKYL HALIDES Section 5.5 BONDING IN ALCOHOLS AND ALKYL HALIDES

Hybridization, Geometry, and Bonding The carbon bonded to –OH or –X is 𝑠𝑝 3 hybridized and tetrahedral The C–O and C–X bonds are polarized toward the more electronegative O or X atom The carbon atom bonded to O or X is partially positive

Dipole Moments Because the C–O and C–X bonds are polarized, alcohols and alkyl halides are polar! Dipole moments are comparable to that of water Note the direction of the dipole vector and the implied partial charges on C, O, and X

Electrostatic Potential Maps In both compounds, the heteroatom bears significant negative charge In methanol, the O–H hydrogen bears most of the positive charge In chloromethane, the nearby C–H hydrogens bear most of the positive charge