Chapter 8

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

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CHAPTER 8 ydroxy Functional Group: Hydroxy Functional Group: Alcohols roperties Preparation and Properties, Preparation, and Strategy of Synthesis
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Ethanol is the alcohol contained in alcoholic beverages. Yeast enzymes 61 26 3 2 2 C H O 2 CH CH OH + 2 CO ⎯⎯⎯⎯⎯→ Alcohols can be thought of as a derivative of water in which a hydrogen atom has been replaced by an alkyl group. Replacement of the 2 nd hydrogen on the water molecule leads to n ether. an ether.
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Naming the Alcohols 8-1 he systematic nomenclature of alcohols treats them as The systematic nomenclature of alcohols treats them as derivatives of alkanes. The –e is dropped from the alkane name and is replaced by –ol. Alkane Æ Alkanol In complicated, branched alkanes, the name of the alcohol is based on the longest chain containing the –OH group. Other substituents are then named using the IUPAC rules for hydrocarbons.
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he number of the chain is from the end closest to the OH group. The number of the chain is from the end closest to the OH group. Cyclic alcohols are called cycloalkanols and the carbon carrying the –OH group is the 1 carbon.
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Alcohols can be classified as primary, secondary or tertiary: In common notation (non-IUPAC), the word alcohol directly follows the name of the alkane. •Methyl alcohol opropyl alcohol •Isopropyl alcohol •Tert-Butyl alcohol
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Structural and Physical Properties of Alcohols 8-2 he structure of alcohols resembles that of water The structure of alcohols resembles that of water. In the structures of water, methanol, and methoxymethane, the oxygen atoms are all sp 3+ hybridized and their bond angles are all nearly tetrahedral. The O-H bond is shorter than the C-H bonds. The bond strength of the O-H bond is greater than that of the C-H bonds: H o 104 kcal mol -1 •DH O-H = 104 kcal mol •DH o C-H = 98 kcal mol -1
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Due to the electronegativity difference between oxygen and ydrogen, the O- bond is polar. hydrogen, the O H bond is polar.
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Hydrogen bonding raises the boiling points and water solubilities of alcohols. Alcohols have unusually high boiling points compared to the corresponding alkanes and haloalkanes. Hydrogen bonding between alcohol molecules is much stronger than the London forces and dipole-dipole interactions in alkanes and haloalkanes, although much weaker than O-H covalent bonds. •O···H-O DH o ~ 5-6 kcal mol -1 ovalent O H 104 kcal mol - •Covalent O-H DH o = 104 kcal mol 1 . The extensive network of H-bonds between neighboring alcohol molecules makes it difficult for a molecule to leave the surface of the liquid. An alcohol molecule makes slightly less than 2 hydrogen bonds to other alcohol molecules on the average. A water molecule, on the other hand, forms hydrogen bonds to slightly less than 4 other water molecules. Water has an abnormally high boiling point for a molecule of its size due to this hydrogen bonding.
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Many alcohols are appreciably soluble in water whereas their parent alkanes are not.
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Chapter 8 - CHAPTER 8 Hydroxy Functional Group: Alcohols...

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