Alcohols Alcohol – any organic compound containing a hydroxyl (R-OH) group Uses: synthetic intermediate, cleanser, cosmetics, fuel, alcoholic beverages, etc. Alcohols are an extremely important organic source Nomenclature For an alcohol the longest continuous chain containing the hydroxy group determines the root name and then an –ol is used as the suffix CH CH OH Ethanol 3 2 In numbering the chain, the hydroxy group takes priority to find the lowest number CH CHOHCH CH 2-Butanol 3 2 3 Priority in Numbering Of substituents learned so far, alcohol has the highest priority OH 4-bromo-2-cyclohexen-1-ol Br Alkenes have higher priority than halides or alkyl substituents 3-bromocyclohexene Br With only halides or alkyl substituents, the lowest number goes to the first substituent 1-bromocyclohexane (1 is not required) Br All other nomenclature is identical to that previously learned There are common names, however, with an aromatic ring Benzene (also called a phenyl group) OH Phenol (takes phenyl root with –ol suffix) Physical Properties There are two physical properties of alcohols that account for their behavior: molecular dipole and hydrogen bonding ability Dipole The electronegative oxygen causes the molecule to have a dipole moment This high dipole-dipole interaction causes alcohols to have a higher affinity for states where the dipoles can be aligned (therefore boiling point is higher) Dipole-dipole interactions, however, are much weaker than hydrogen bonding interactions A hydrogen bond is an interaction between a weakly acidic hydrogen and a lone pair of electrons on a different atom Each hydrogen bond has an energy of ~4-5 Kcal/mol This is much smaller than a covalent bond (O-H ~ 104 Kcal/mol) but a compound can have multiple hydrogen bonds that need to be broken to “escape” the liquid phase (i.e. causes a higher boiling point) Due to this hydrogen bonding ability of alcohols they are both hydrophilic and hydrophobic Hydrophilic – “water loving” Hydrophobic – “water hating” Due to this property alcohols have a high water miscibility until the carbon chain becomes larger Methanol versus Ethanol Biochemically Ethanol (which is known to lower inhibitions and cause a lightheadedness) is oxidized biochemically to acetaldehyde alcohol aldehyde O O dehydrogenase dehydrogenase H O H OH The physiological side effects of consuming ethanol are due to the buildup of acetaldehyde (causes nausea, dizziness, seating, headaches, lower blood pressure) The acetaldehyde is then oxidized biochemically to acetic acid Some people have a nonfunctioning aldehyde dehydrogenase enzyme -these people experience the side effects of acetaldehyde with low ethanol consumption Methanol also gets oxidized by the same enzyme alcohol O dehydrogenase H O H H But due to one less carbon, this oxidation creates formaldehyde not acetaldehyde Formaldehyde is toxic to the body because it disrupts other essential enzymes form working properly Ethanol is consumed ~25 times faster than methanol by this enzyme Acidity of Alcohols The alcohol O-H bond is weakly acidic We have already seen the use of alkoxides in substitution reactions CH ONa sodium methoxide 3 The alkoxides can be generated by reaction of an alcohol with sodium hydride