Properties of alcohols
Alcohols are characterized by a number of physical and chemical properties:
- Intense aroma
- Hydrogen bonds
The first ten alcohols, which have molecules with shorter hydrocarbon chains, are characterized by being transparent substances . They are physically and chemically very similar to water, so they even look similar. On the other hand, these first alcohols have very penetrating aromas ; some pleasant, some irritating.
The first alcohols, which are presented in liquid form, are characterized by having a low density , so if they are put in a container with water, a quantity of alcohol will remain floating on top of the watery bottom. The same goes for oils, which are noticeable as a yellowish coating on top of the transparency of the water.
Liquid alcohols are volatile , that is, they have a boiling point below 100 ° C, which corresponds to that of water. They even tend to evaporate to a great extent when exposed to room temperature. What partially retards this evaporation are intermolecular forces called ” hydrogen bonding “.
Hydrogen bridging bonds by attraction the hydrogens of the hydroxyl groups (-OH) of the alcohol molecules that are closest to each other, helping to increase the boiling point and density of the substance. Finally, alcohols have a degree of toxicity . For example, drinking 500mL of pure ethanol is deadly for almost anyone.
Nomenclature of alcohols
To give the IUPAC name of an alcohol, simply add the letter “l” to the end of the name of the alkane it comes from. Thus, for CH 3 OH the corresponding name is Methanol , and for CH 3 CH 2 OH the name is Ethanol . Propanol has 2 isomers: CH 3 CH 2 CH 2 OH , which is 1-propanol, since -OH is on the first carbon; and CH 3 -CH (OH) -CH 3 , which is 2-propanol.
In 2-propanol, the hydroxyl group is attached to the central carbon. Commonly, it is known by another name, which is Isopropanol . In 70% aqueous solution, it is used as rubbing alcohol. There are also four isomers for butanol, which are butanol, isobutanol, secbutanol, tertbutanol. Parentheses indicate a branch.
- Butanol: CH 3 CH 2 CH 2 CH 2 OH
- Isobutanol: CH 3 -CH (CH 3 ) -CH 2 OH
- Secbutanol: CH 3 CH 2 -CH (OH) -CH 3
- Terbutanol: (CH 3 ) 3 -COH
The common name of an alcohol is written in the following format:
Word “alcohol” + name of the radical R + “ico”
For example, for CH 3 OH, the name is:
CH 3 OH: Alcohol + Methyl + “ico”
CH 3 OH: Methyl Alcohol
For CH 3 CH 2 OH, the name is:
CH 3 OH: Alcohol + Ethyl + “ico”
CH 3 OH: Ethyl alcohol
Types of alcohols
Alcohols have two criteria to be classified:
- The position of the hydroxyl group in the chain
- The number of hydroxyl groups in the chain
Types of alcohols by the position of OH
Alcohols, depending on the position in which the hydroxyl group is, can be classified into three categories:
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
The primary alcohols have the hydroxyl group (-OH) attached to the carbon that is only linked to a carbon (CH 3 or CH 2 ). The straight chain alcohols are primary.
CH 3 OH Methanol
CH 3 CH 2 OH Ethanol
CH 3 CH 2 CH 2 OH Propanol
The secondary alcohols have the hydroxyl group (-OH) attached to the carbon which is bonded to two carbons (CH). These alcohols are generally branched.
CH 3 -CH (OH) -CH 3 Isopropanol
CH 3 CH 2 -CH (OH) -CH 3 Secbutanol
The tertiary alcohols have a hydroxyl group (-OH) attached to the carbon that is bonded to three carbons (C). These alcohols have the carbon completely surrounded.
(CH 3 ) 3 -COH Terbutanol or trimethylmethanol
CH 3 CH 2 (CH 3 ) 2 COH 1,1-dimethyl propanol
Types of alcohols by the number of OH
Alcohols, according to the number of hydroxyl groups they have in their molecule, are classified as:
- Simple alcohols
The simple alcohols are those which have only one hydroxyl group.
CH 3 CH 2 CH 2 OH Propanol
CH 3 CH 2 CH 2 CH 2 OH Butanol
The diols are those alcohols having two hydroxyl groups.
HO-CH 2 CH 2 -OH Ethanediol or Glycol
HO-CH 2 CH 2 CH 2 -OH Propanediol
The triols are those alcohols having three hydroxyl groups.
HO-CH 2 -CH (OH) -CH 2 OH Propanetriol or Glycerol
CH 3 -CH (OH) -CHOH-CH 2 OH Butanetriol
Some examples of alcohols are as follows. The parentheses indicate that there are multiple terms (CH 2 ) in the chain. The number of them is said with a subscript outside the parentheses.
- Methanol CH 3 OH
- Ethanol CH 3 CH 2 OH
- Propanol CH 3 CH 2 OH
- Butanol CH 3 CH 2 CH 2 CH 2 OH
- Pentanol CH 3 (CH 2 ) 4 OH
- Hexanol CH 3 (CH 2 ) 5 OH
- Heptanol CH 3 (CH 2 ) 6 OH
- Octanol CH 3 (CH 2 ) 7 OH
- Nonanol CH 3 (CH 2 ) 8 OH
- Decanol CH 3 (CH 2 ) 9 OH
- Undecanol CH 3 (CH 2 ) 10 OH
- Ethanediol HOCH 2 CH 2 OH
- 1,3-Propanediol HOCH 2 CH 2 CH 2 OH
- 1,4-Butanediol HOCH 2 CH 2 CH 2 CH 2 OH
- 1,5-Pentanediol HOCH 2 (CH 2 ) 3 CH 2 OH
- 1,6-Hexanediol HOCH 2 (CH 2 ) 4 CH 2 OH
- 1,7-Heptanediol HOCH 2 (CH 2 ) 5 CH 2 OH
- 1,8-Octanediol HOCH 2 (CH 2 ) 6 CH 2 OH
- 1,9-Nonanediol HOCH 2 (CH 2 ) 7 CH 2 OH
- 1,10-Decanediol HOCH 2 (CH2) 8 CH 2 OH