CH 10 - Alcohols and Thiols

alcohol

-OH group bonded to a sp3 carbon

alcohol bond angle

109.5

alcohol nomenclature - parent chain

the longest carbon chain that contains the -OH group

alcohol nomenclature suffix

-ol

• propanol

alcohol common names - methanol

wood alcohol

alcohol common names - ethanol

alcohol = grain alcohol

alcohol common names - 2-propanol

isopropyl alcohol = isopropanol

alcohol common names - 1,2-ethanediol

ethylene glycol = antifreeze

1,2,3-propanetriol

glycerol = glycerine

alcohol nomenclature - alcohol and alkene

• use both alkene and alcohol endings (-ene- and -ol)

• alcohol has priority in numbering over alkene

polarity of the C-O-H in an alcohol

dipole-dipole interactions and hydrogen bonding

dipole-dipole interaction

the attraction between the positive end of one dipole and the negative end of another

hydrogen bonding effects on boiling point

increases it significantly

in relation to hydrocarbons, alkyl halides, and ethers of comparable sizes and molecular weight, alcohols

• have higher boiling points

• are more soluble in water

the presence of additional -OH groups in a molecules further increases

solubility in water and boiling point

stronger interactions =

higher boiling/melting points

alcohols are

moderate acids

alcohols react with Li, Na, K and other active metals to

liberate hydrogen gas and form metal alkoxides

alcohols are also converted to metal alkoxides by reaction with

bases stronger than the alkoxide ion (NaH)

PBr3 reaction

replaces OH with Br

SOCl2 reaction

replaces OH with Cl

sulfonate esters are prepared from reaction of

sulfonyl chlorides and alcohols

sulfonic acids are very

strong acids

sulfonates are

weak bases

sulfonates are great

leaving groups

one commonly used sulfonate is

p-toulenesulfonate (tosylate, TsO-)

another commonly used sulfonate is

methanesulfonate (mesylate, MsO-)

sulfonate formation does not

change alcohol configuration

• S → S

subsequence Sn2 reaction

inverts configuration

• S → R

oxidation of a primary alcohol gives an

aldehyde or carboxylic acid, depending on the experimental condition

oxidation to an aldehyde is

a two-electron oxidation

oxidation to a carboxylic acid is a

four-electron oxidation

primary alcohols - strong oxidants such as chromic acid (H2CrO4) stop

at carboxylic acid, no aldehyde

oxidation of a secondary alcohol gives

a ketone in a two-electron oxidation

tertiary do

not undergo oxidations

• short of combustion

stern oxidation avoids

Cr(VI) species that are carcinogenic and stops at aldehyde for primary alcohols

swern oxidation reagents

1. DMSO/oxalyl chloride

2. Et3N

primary alcohol - PCC

stops at aldehyde

primary alcohol - dess martin (DMP)

stops at aldehyde

oxidation of glycols (1,2-diols) uses

periodic acid

oxidation of glycols (1,2-diols)

1. bond between -OH groups cleaved

2. aldehydes added where -OH are

the functional group of a thiol is

an -SH group bonded to a sp3 carbon

bond angle of thiol

100.3

thiol nomenclature - IUPAC parent chain

the longest carbon chain containing -SH group

thiol nomenclature - IUPAC ending

-ethiol

thiol nomenclature - IPUAC substituents

sulfanyl group

thiols compared to alcohols

lower boiling points, and less soluble in water

thiols and constitutional isomer properties

almost identical

thiols are stronger acids than

alcohols

when dissolved in an aqueous NaOH, thiols are converted completely to

alkyl sulfide salts

thiols preparation - the most common preparation of thiols depends on

the very high nucleophiliticy of HS-

a thiol can be oxidized to

• disulfide (R-S-S-R)

• sulfinic acid (like a carboxylic acid)