Ch10 - Synthesis and Structure of Alcohols Alcohols can be...

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Synthesis and Structure of Alcohols Alcohols can be considered organic analogues of water. H O HR O H Alcohols are usually classified as primary, secondary and tertiary. R H H OH R H R OH R R R OH primary secondary tertiary OH phenol Alcohols with the hydroxyl bound directly to an aromatic (benzene) ring are called phenols. Nomenclature of Alcohols (Normally any compound’s name which ends in –ol is an alcohol of some sort) IUPAC rules that: (1) Name the longest carbon chain bearing the –OH group. Drop the last –e from the alkane name and add –ol to obtain the root name. (2) Number the longest chain starting at the end nearest the –OH group, and designate a number for the –OH group. (Hydroxyl has greater priority than carbon-carbon multiple bonds). (3) Name the remaining substituents and their numbers as for alkanes and alkenes. H 3 C CH 3 CH 3 OH H CH 2 -Cl 1-chloro-3,3-dimethyl-2-butanol Ch10 Alcohols (Str and Syn) Page1
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(4) Cyclic alcohols have the prefix cyclo-, and the hydroxyl group is deemed to be on C-1. HO CH 2 CH 3 1-ethylcyclopropanol (5) Alcohols with double or triple bonds are named using the –ol suffix on the alkene or alkyne name. Numbering gives the hydroxyl group the lowest possible number. When numbers are also given for the multiple bond position, the position of the hydroxyl can be written immediately before the –ol prefix. Cl H H OH H 3 C (Z)-4-chloro-3-buten-2-ol (6) If the hydroxyl group is only a minor part of the structure, it may be named as a hydroxy- substituent. CO 2 H OH 3-hydroxybutanoic acid Nomenclature of Diols (Gycols) Diols are compounds with two hydroxyl groups. They are named as for alcohols except the suffix –diol is used and two numbers are required to locate the –OH’s. OH OH 1-cyclohexyl-1,3-butanediol Ch10 Alcohols (Str and Syn) Page2
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Nomenclature of Phenols A phenol always involves a benzene (type) ring, and often the terms ortho, meta and para (meaning 1,2 disubstituted, 1,3 disubstituted and 1,4 disubstituted respectively) are used. These terms are non-IUPAC though. OH Br OH CH 3 OH NO 2 2-bromophenol ortho-bromophenol 3-methylphenol meta-methylphenol 4-nitrophenol para-nitrophenol Solubility of Alcohols The hydroxyl groups in alcohols can form hydrogen bonds with water, and many low molecular weight alcohols are miscible with water. Alcohols are more polar than hydrocarbons, and are better solvents for polar substances. (E.g. NaCl is partially soluble in Ethanol). The Hydroxyl group is said to be hydrophilic (water loving), whereas the alkyl (hydrocarbon) end is hydrophobic (water hating). Alcohols will also dissolve in hydrocarbon solvents. Acidity of Alcohols and Phenols Just like water, the hydroxyl groups in alcohols are weakly acidic – strong bases can generate alkoxide ions.
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Ch10 - Synthesis and Structure of Alcohols Alcohols can be...

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