Alcohols د. جهاد الماليطي

Structure - Alcohols Alcohols R-O-H The functional group of an alcohol is an -OH group bonded to an sp3 hybridized carbon bond angles about the hydroxyl oxygen atom are approximately 109.5° Oxygen is sp3 hybridized two sp3 hybrid orbitals form sigma bonds to carbon and hydrogen the remaining two sp3 hybrid orbitals each contain an unshared pair of electrons Draw the orbitals of CH3OH

Classification A primary (1°) alcohol is one in which the carbon atom with the OH group is attached to one other carbon atom (in blue). Its general formula is RCH2OH. A secondary (2°) alcohol is one in which the carbon atom with the OH group is attached to two other carbon atoms (in blue). Its general formula is R2CHOH. A tertiary (3°) alcohol is one in which the carbon atom with the OH group is attached to three other carbon atoms (in blue). Its general formula is R3COH. Aromatic (phenol): -OH is bonded to a benzene ring.

Nomenclature-Alcohols IUPAC names the parent chain is the longest chain that contains the OH group number the parent chain to give the OH group the lowest possible number change the suffix -e to -ol IUPAC names for simple Unbranched Alkyl Name Molecular Formula Structural Formula methane CH4 hexane C6H14 CH3(CH2)4CH3 ethane C2H6 CH3CH3 heptane C7H16 CH3(CH2)5CH3 propane C3H8 CH3CH2CH3 octane C8H18 CH3(CH2)6CH3 butane C4H10 CH3CH2CH2CH3 nonane C9H20 CH3(CH2)7CH3 pentane C5H12 CH3(CH2)3CH3 decane C10H22 CH3(CH2)8CH3

Nomenclature-Alcohols Common names name the alkyl group bonded to oxygen followed by the word alcohol

Nomenclature-Alcohols Examples

Nomenclature of Alcohols Compounds containing more than one OH group are named diols, triols, etc. For common Names: 1, 2 diols (vicinal diols) are called glycols. C H 3 2 C H 2 C H 2 O H O H H O O H H O H O O H 1,2-Ethanediol (Ethylene glycol) 1,2-Propanediol (Propylene glycol) 1,2,3-Propanetriol (Glycerol, Glycerine)

Nomenclature of Alcohols Unsaturated alcohols show the double bond by changing the infix from -an- to -en- show the the OH group by the suffix -ol number the chain to give OH the lower number

Nomenclature of Alcohols - Naming Priority 7- Alkenes 8- Alkynes 9- Alkanes 10- Ethers 11- Halides 1- Acids 2- Esters 3- Aldehydes 4- Ketones 5- Alcohols 6- Amines Don’t worry about this

Nomenclature of Alcohols When -OH is part of a higher priority class of compound, it is named as hydroxy. Example: 4-hydroxybutanoic acid

Naming Phenols -OH group is assumed to be on carbon 1. For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4. Methyl phenols are cresols. 4-methylphenol para-cresol 3-chlorophenol meta-chlorophenol

Physical Properties Alcohols are polar compounds they interact with themselves and with other polar compounds by dipole-dipole interactions Dipole-dipole interaction: the attraction between the positive end of one dipole and the negative end of another

Physical Properties Hydrogen bonding: when the positive end of one dipole is an H bonded to F, O, or N (atoms of high electronegativity) and the other end is F, O, or N the strength of hydrogen bonding in water is approximately 21 kJ (5 kcal)/mol hydrogen bonds are considerably weaker than covalent bonds nonetheless, they can have a significant effect on physical properties

Physical Properties Ethanol and dimethyl ether are constitutional isomers. Their boiling points are dramatically different ethanol forms intermolecular hydrogen bonds which increase attractive forces between its molecules resulting in a higher boiling point there is no comparable attractive force between molecules of dimethyl ether C H 3 2 O C H 3 O Ethanol Dimethyl ether bp 78° C bp -24°C

Physical Properties In relation to alkanes of comparable size and molecular weight, alcohols have higher boiling points are more soluble in water The presence of additional -OH groups in a molecule further increases solubility in water and boiling point

Physical Properties

Acidity of Alcohols In dilute aqueous solution, alcohols are weakly acidic Ka acid dissociation constant

Acidity of Alcohols

Acidity of Alcohols pKa range: 15.5-18.0 (water: 15.7) Acidity decreases as alkyl group increases. Halogens increase the acidity. Phenol is 100 million times more acidic than cyclohexanol!

Table of Ka Values =>

Formation of Alkoxide Ions React methanol and ethanol with sodium metal (redox reaction).

Formation of Phenoxide Ion Phenol reacts with hydroxide ions to form phenoxide ions - no redox is necessary. O H O + O H + H O H p K = 1 5 . 7 a p K = 1 a