CHM 25500 Lecture Notes - Lecture 32: Thiol, Acid Dissociation Constant, Hydrogen Bond
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5 Aug 2015
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CHM 255 - Lecture 32 - Alcohols and Thiols
Definitions
● Alcohols are compounds that contain hydroxyl groups (OH) attached to an sp3
hybridized carbon
● Thiols are compounds that contain sulfhydryl groups (SH) attached to an sp3
carbon
Nomenclature
● The parent chain in an alcohol is the longest chain that contains the hydroxyl
group
● The ‘e’ on the end of the name of the alkane is replaced with ‘ol’
● Hydroxyl groups always take precedence over other groups (including double
and triple bonds) when numbering the carbons
○ When numbering cyclic alcohols the numbering always starts with the
carbon attached to the hydroxyl group
Physical Properties
● When compared to simple hydrocarbons, alcohols have relatively high boiling
points for their molecular weights
○ This is because of the type of intermolecular interactions that take place
between the molecules
● In simple hydrocarbons, there are only induced dipole interactions between the
molecules
● In alcohols, however, there are induced dipole interactions as well as permanent
dipole-dipole interactions and hydrogen bonding that occur between the
molecules
Acidity of Alcohols and Thiols
● Alcohols can function as either weak acids or weak bases
● Most alcohols have a pKa of around 16-18
● When alcohols are deprotonated it results in an alkoxide ion (strong base)
● Alcohols may be protonated by strong acids
○ When this happens water is produced, which is a very effective leaving
group