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Unformatted text preview: Chapter 8: Hydroxy Functional Group: Alcohols Properties, Preparation, and Strategy of Synthesis • Alcohols have carbon backbones with hydroxy functional groups (OH) 8.1. Naming the Alcohols • “alkanols”: replace –e with –ol • Name longest chain containing the OH substituent group • Number each carbon atom beginning from end closest to OH group; other substituents are added to alkanol stem as prefixes • Cyclic alcohols are cycloalkanols; carbon carrying OH group receives number 1 • If OH group is substituent, it is called hydroxy , this occurs only when there are functional groups that take higher precedence (i.e., hydroxycarboxylic acids) • Primary, secondary, and tertiary alcohols are classified by number of carbons the carbon with the OH group is attached to • Common nomenclature: alkyl alcohol, don’t use! 8.2. Structural and Physical Properties of Alcohols • Allows hydrogen bonding raise boiling points, increase solubility in water • The structure of alcohols resembles that of water o Oxygen is sp 3 hybridized (like ammonia and methane), almost tetrahedral bond angles o O-H bond shorter and thus stronger than C-H bond because of high electronegativity of oxygen relative to carbon; electronegativity determines how tightly nuclei hold onto surrounding electrons • Hydrogen bonding raises the boiling points and water solubilities of alcohols o Alcohols have higher boiling points than alkanes and haloalkanes because of hydrogen bonding o Hydrogen bonding results in an extensive network of these interactions o Water’s hydrogen bonding ability is increased by having two hydrogens and as a result, boils at 100 degrees Celsius o Haloalkanes are poorly soluble in water because they are hydrophobic whereas alcohols are much more soluble because they are hydrophilic o Solubility of alcohols in water decrease as alkyl chain increases 8.3. Alcohols as Acids and Bases • The acidity of alcohols resembles that of water o Alcohols, like water, are fairly weak acids; but acidity is greater than alkanes and haloalkanes o St rong elect ronegativity of oxygen stabilizes the negative charge of the alkoxide ion • Steric disruption and inductive effects control the acidity of alcohols o Acidity decreases (pK a increases) from methanol to primary, secondary, and tertiary systems o Solvation and hydrogen bonding stabilize negative charge on oxygen; on tertiary systems, there is greater steric disruption to solvation and hydrogen bonding o Presence of halogens increases acidity...
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This note was uploaded on 09/21/2010 for the course CHEM Chemistry taught by Professor Nitche during the Spring '08 term at Berkeley.
- Spring '08