Chapter 8 - Hydroxy Functional Group- Alcohols

Chapter 8 - Hydroxy Functional Group- Alcohols - Chapter 8...

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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
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o Strong electronegativity 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 o
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