Organic Chemistry: Alkyl Halides and Alcohols Notes

1.1 Learning Objectives

• Understand the structures and nomenclature of alkyl halides and alcohols according to IUPAC rules.

• Be able to predict products of reactions involving these compounds.

• Distinguish between primary, secondary, and tertiary alcohols through various tests.

1.2 Alkyl Halides

• Definition: Alkyl halides (haloalkanes) are organic compounds containing a carbon-halogen bond, represented as RX where X can be F, Cl, Br, or I.

• General Formula: CnH{2n+1}X

• Bond characteristics:

  • Bond lengths increase with halogen size: C-I > C-Br > C-Cl > C-F.

  • Bonding involves sp³ hybridization with tetrahedral geometry.

1.3 Synthesis of Alkyl Halides

• Common reagents include:

  • Hydrohalic acids (HBr, HCl)

  • Phosphorus trichloride (PCl₃) / PCl₅ / thionyl chloride (SOCl₂).

• Example Reaction:

  • CH3-CH2-OH + HCl
    ightarrow CH3-CH2-Cl + H_2O

1.4 Chemical Reaction of Alkyl Halides & Mechanisms

• Nucleophilic Substitution: Two types:

  • SN1 Reaction:

  • Steps:

    1. Ionization to form a carbocation.

    2. Nucleophile attacks the carbocation.

  • SN2 Reaction:

  • Direct attack of nucleophile leads to simultaneous bond breaking.

• Example Mechanism for SN2:

  • CH3-CH2-Cl + OH^-
    ightarrow CH3-CH2-OH + Cl^-

1.5 Alcohols (R-OH)

• Structurally: Composed of carbon chains with a hydroxyl (-OH) functional group.

• Naming Protocol:

  • Identify the longest carbon chain containing -OH as the main chain.

  • Numbering should prioritize the -OH group.

• Common alcohols include:

  • Methanol (1 carbon), Ethanol (2 carbons), and so forth.

1.6 Structure and Physical Properties of Alcohols

• Alcohols are polar due to the hydroxyl group and capable of hydrogen bonding, resulting in higher boiling points compared to alkanes.

• As carbon chain length increases:

  • Boiling points rise due to stronger van der Waals forces and increased hydrogen bonding.

  • Miscibility in water decreases, especially above 6 carbon atoms.

1.7 Synthesis of Alcohols

/

• Methods include:

  • Hydration of Alkenes:

  • RCH=CHR' + H_2O
    ightarrow RCH(OH)R' (hydration requires conditions like acid catalysis).

  • Reduction of Aldehydes/Ketones:

  • Uses reducing agents (LiAlH₄ or NaBH₄).

1.8 Chemical Reactions of Alcohols

• Combustion: Complete oxidation of alcohols forms carbon dioxide and water.

• Oxidation: Primary and secondary alcohols can be oxidized to aldehydes/ketones, then to carboxylic acids. Tertiary alcohols resist oxidation.

• Formation of Esters:

  • R-OH + R'COOH
    ightarrow R'O-R + H_2O (Fischer esterification).

• Dehydration: Alcohols can lose water to form alkenes.

1.9 Summary

• Alkyl halides and alcohols are vital organic compounds with unique properties and many reactions.

• The synthesis and reaction mechanisms are important for understanding their applications in organic chemistry.

• Tests for characterizing these compounds include oxidation and precipitation tests.