15.1 Alcohols Flashcards
What is the functional group of an alcohol
Are they reactive
They have functional group -OH attached to a hydrocarbon chain
General formula CnH2n+1OH
Yes, they are reactive
When naming alcohols, what is the suffix
What would the prefix be if it were used
The suffix -ol is used usually
But sometimes the prefix hydroxy- is used if there are other functional groups present
What is the name of the alcohol form of butane
Butanol
But if the OH is attached to the first or last carbon, it is Butan-1-ol
If the OH is attached to the 2nd or 3rd, it is butan-2-ol
If there is more than one OH group, how do you say this in the name
So if butane had two alcohol groups on the first and last carbon, what would it be called
What is propane had alcohol group on 1,2,3 carbon
Di, tri, tetra and so on
Butan-1,4-diol
Propan-1,2,3-triol
What is the shape in alcohols between the carbon, and OH group
The oxygen atom has two bonding pairs and two lone pairs
As it is bonded to one carbon and one hydrogen
So tetrahedral is the shape, but bond angles are 104.5 degrees, as the angle decreases as lone pairs repel each-other more than bond pairs
So this is the angle between carbon and oxygen
How are alcohols classified
They are classified as primary (1), secondary(2) and tertiary (3)
According to how many other groups are bonded to the carbon that has the OH group
These other groups are alkyls, or other carbon atoms
Why is propan-1-ol a primary alcohol
Why is methanol a primary alcohol
The OH group is attached to the end carbon, so that carbon is only attached to one other, and two hydrogens (which don’t count as alkyl groups)
There is only one carbon in the molecule and it is bonded to the OH group, and there are no R groups so it is counted as a primary alcohol.
So they are primary if the carbon attached to OH group is only binded to one other
So primary alcohols always have an OH at the end of the chain
Why is propan-2-ol a secondary alcohol
The OH group is attached to a carbon which is bonded to two other alkyl groups (other carbon atoms which themselves are attached to hydrogens)
So in alcohols, the OH is always bonded to the body of the chain, so in the middle
Why is 2-methylpropan-2-ol a tertiary alcohol
These alcohols have three R groups attached to the carbon with the OH
So the OH is in a branch
Why do alcohols have higher melting points than alkanes
The OH- has hydrogen bonding in it between the molecules so more heat energy is required to break these intermolecular forces.
Are alcohols soluble in water
How does it depend on size
The OH- group of alcohols can hydrogen bond with water molecules, but the non-polar part of the chain can’t
So alcohols with short hydrocarbon chains are soluble in water because the hydrogen bonding predominates
In longer chain alcohols however, the non polar hydrocarbon chain dominates so the alcohol is insoluble in water
