11 - alcohols Flashcards
What is the alcohol functional group?
OH (Hydroxyl group)
What is the general formula of alcohols?
C~n H~(2n + 2) O
When is an alcohol a primary alcohol?
When the OH is only attached to one alkyl group.
When is an alcohol secondary?
When the carbon that the OH is on is attached to two alkyl groups
When is an alcohol tertiary?
When the carbon that the OH is on is attached to three alkyl groups
What state does ethanol have at room temperature?
liquid
Why do alcohols have a higher boiling point than alkanes?
The OH group has a dipole (H has delta positive)
What is volatility?
How easily a substance evaporates
How does volatility change as boiling point changes?
Volatility decreases as boiling point increases
What is the volatility of alcohols like compared to alkanes and why?
alcohols have a low volatility compared to alkanes
Due to hydrogen bonds
Do alcohols dissolve in water?
Explain
They do dissolve in water
Because they are polar due to their hydrogen bonds
How does chain length affect solubility and why?
As chain length increases, solubility decreases
Because hydrocarbon chain is not polar and can’t make hydrogen bonds with water
What is an oxidising agent?
A reagent which provides the oxygen in a reaction
In the oxidation of alcohols
What is the oxidising agent?
Acidified potassium dichromate
H+ | K~2 Cr~2 O~7
What are the 2 oxidation reactions that can be done on primary alcohols?
Distillation
Reflux
What is formed when primary alcohols are oxidised by distillation?
Aldehyde and water
How do you draw aldehydes?
One of the END carbons must have a C=O instead of one if its C-H bonds
How do you write the equation for the oxidation of an alcohol by distillation?
Draw out the alcohol
Then put + [O]
Then draw the reaction arrow with H+ | K~2 Cr~2 O~7 above it and “distillation” below it
Draw the aldehyde with the same number of carbons as the alcohol
Then put + H~2 O
What are the observations of all primary alcohol oxidation reactions?
Acidified potassium dichromate goes from orange to green
What is the naming system for aldehydes?
- al suffix
e. g. Ethanol goes to ethanal
What is the aldehyde functional group?
CHO
What is produced when alcohols are oxidised by reflux?
Carboxylic acid and water
What type of alcohol do you need to use to get carboxylic acids?
A primary alcohol must be used under reflux
How do you draw carboxylic acids?
Put a C-OH
And C=O
On the end carbon
How do you write the equation for reflux oxidising alcohols?
Draw the alcohol
Put + 2[O]
Draw the reaction arrow with H+ | K~2 Cr~2 O~7 above and reflux below
Draw the carboxylic acid
Write + H~2 O
What is the functional group of carboxylic acids?
COOH
What is the observation when oxidising secondary alcohols?
Still colour change from orange to green
What is a ketone?
Like an aldehyde but the C=O is on a middle carbon (not end carbon)
when finding an isomer of a ketone, you can’t put the C=O on an end carbon because that would be an aldehyde
What is the functional group for ketones?
RCOR
R just means other stuff (usually an alkyl group)
What are the types of reaction for oxidising secondary alcohols?
There’s only one
Applying heat
How do you name ketones?
- one is the suffix
e. g. pentan-2-one
How do you write the reaction for oxidation of secondary alcohols?
Draw an alcohol where the OH isn’t on an end carbon
Put + [O]
Put a reaction arrow with H+ | K~2 Cr~2 O~7 above it and “heat” below it
Draw the ketone
Put + H~2 O
Describe the dehydration of alcohols
An alcohol is heated with a reagent of CONCENTRATED H~2 SO~4 and heat
An alkene and water is produced
This is an elimination reaction
With dehydration of alcohols, what is different when secondary alcohols are used?
2 different alkenes are produced
With the double bond on the left of where the OH was
And with the double bond on the right of where the OH was
What is the basic idea of what happens in an alcohol substitution reaction?
The OH of the alcohol is substituted by a halogen to form a haloalkane
What are the conditions and reagents of alcohol substitution?
Reflux the alcohol
With sulphuric acid and sodium halide
(The halide contains the halogen that we want in the haloalkane)
Why is a sodium halide used in substitution of alcohols?
The hydrogen halide on its own doesn’t work for some reason
What is the first reaction which happens in substitution of alcohols?
NaX + H~2 SO~4
–>
NaHSO~4 + HX
Where X is the halogen
What is the second reaction which happens in substitution of alcohols?
Use ethanol as the alcohol
C~2 H~6 O + HX
–>
C~2 H~5 X + H~2 0
Where X is the halogen
What is the overall reaction of alcohol substitution?
Use propanol as the alcohol and chlorine as the halogen
C~3 H~8 O + NaCl + H~2 SO~4
–>
C~3 H~7 Cl + NaHSO~4 + H~2 O
What does a nitrile contain?
A triple bond
How do you draw cyanide?
C triple bond N
Put a lone pair on the C
Why are the boiling points of branched alcohols less than boiling points of straight chain alcohols?
2 marks
Less points of contact between branched alcohols
So less energy required to break London forces in branched alcohols
