In chemistry, an alcohol is any organic compound in which a
hydroxyl group (-OH) is bound to
a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is
formed by the simple acyclic alcohols, the general formula for which is
CnH2n+1OH.
After the nature of the hydrocarbons radical (the radical connected to the –OH group),
you can distinguish several types of alcohol:
- if the radical derives from a
saturated hydrocarbon (acyclic or cyclic),
the respective alcohol is a
saturated alcohol (for example: ethanol CH
3-CH
2-OH).
- if the radical has a
double bound, the respective alcohol is a
unsaturated alcohol
(for example: allelic alcohol CH
2=CH-CH
2OH).
- if the radical contains an
aromatic nucleus, the respective alcohol is a
aromatic
alcohol (for example: benzilic alcohol C
6H
6-CH
2OH).
There are three major subsets of alcohols:
primary (1°),
secondary (2°)
and
tertiary (3°), based upon the number of carbon atoms the C-OH group's carbon
is bonded to.
Ethanol is a simple 'primary' alcohol. The simplest secondary alcohol
is
isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is
tert-butyl alcohol
(2-methylpropan-2-ol).
The alcohols containing 2 hydroxyl groups connected by different carbon atoms
are called
glycols, for example: CH
2OH-CH
2OH.
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All alcohols contain the hydroxyl functional group,
-O-H, attached to
single bonded hydrocarbons (alkanes). Alcohol have the general formula
R-OH where R represents any chain of carbon and hydrogen atoms.
The four most common alcohols are:
Alcohols use the same formats as alkanes. To name alcohols,
• Determine the
parent chain. The parent chain must be the longest that includes the carbon holding the OH group.
• Number according to the end closest to the -OH group regardless of where alkyl substituents are.
• The format is as follows:
(location of branch)-(branch name)-(location of OH group)-(parent chain)
• Change the parent chain
-e ending and replace it with an
-ol.
Example:
Parent chain: Butane
-OH group location: 2
Substituents locations: 3-methyl
Alkane name: 3-methylbutane
Alcohol name: 3-methyl-2-butanol
Alchohols containing more than one hydroxyl group are also called
polyalcohols.
Polyalcohols are named similarly to alcohols, with the exception of the prefix
di-,
tri-, etc before the -ol ending.
The denomination of an alcohol must take into the consideration the position of the
carbon atom (the one connected to the hydroxyl) and the existence of isomers.
For example, taking into consideration the existence of 2 propanols, they
are designated as 1-propanol and 2-propanol:
CH3-CH2-CH2OH (1-propanol)
CH3-CH(OH)-CH3 (2-propanol)
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