Alcohols, Alkanoic acids and Esters Flashcards
(34 cards)
What is
a primary alcohol?
This is an alcohol that has 1 alkyl group attached to the carbon bearing the -OH group.
It can be represented as: RCH2OH
What is
a secondary alcohol?
This is an alcohol that has 2 alkyl groups attached to the carbon bearing the -OH group.
It can be represented as: RR’CHOH
What is
a tertiary alcohol?
This is an alcohol that has 3 alkyl groups attached to the carbon bearing the -OH group.
It can be represented as: RR’R”COH
Can tertiary alcohols be oxidised?
No
This can be used as a differentiating test btw primary and secondary alcohols from tertiary alcohols. The 2 turn acidified K2Cr2O7 solution green its original orange to but the latter shows no colour change
Why can’t tertiary alcohols be oxidised?
Oxidation is also the removal of hydrogen, in a tertiary alcohol, there is no more hydrogen to be removed
They cannot be oxidised without the breakage of a C-C bond which requires a lot of energy
What reactions do alcohols undergo?
- Oxidation
-
Dehydration (to an alkene)
3.
How are alcohols formed?
- By hydration of an alkene
- By the reaction of water or OH- and a haloalkane
- By fermentation
What kind of reaction
is the hydration of alkenes to form alcohols called?
An electrophilic substitution reaction
What kind of reaction
is the formation of alcohols from halogenoalkanes called?
A nucleophilic substitution reaction
If the nucleophilic substitution reaction
was said to take on the SN1 mechanism, what can one expect in the slow step?
The carbocation is formed first before nucleophilic attack occurs
If the nucleophilic substitution reaction
was said to take on the SN2 mechanism, what can one expect in the slow step?
The C-X bond breaks as the carbon froms the bond with the nucleophile
What kind of alcohol
can be formed from the nucleophilic substitution of haloalkanes using the SN2 mechanism?
A primary or secondary alcohol
What kind of alcohol
can be formed from the nucleophilic substitution of haloalkanes using the SN1 mechanism?
A tertiary or secondary alcohol
What are the reaction conditions (reagents, catalyst, products)
for the formation of alcohols from halogenoalkanes called?
- REAGENTS: The halogenoalkane and NaOH/KOH
- SOLVENT: Water (an aqueous solution)
- PRODUCT: An alcohol and the sodium halide
the OH- group is the nucleophile in this case, however, water can also be used as a nucleophile, in that case a hydrogen halide would be formed
What happens when an ethanolic solution of NaOH/KOH is used for the reaction with halogenoalkanes?
An elimination reaction occurs and an alkane is formed instead
The carbon bearing the C-X bond looses the Halogen and one of the carbons beside it loses one Hydrogen atom, the C=C bond is formed between these two carbons
What does the (Na)OH- acts as in this case, water is formed from it and the hydrogen taken from one carbon
A base
The OH- accepts the liberated hydrogen to form water.
What is there to note
about the nature of the haloalkane before choosing water or NaOH as your reactant?
Its solubility in water
What are the reaction conditions
for the hydration of an alkene?
The reaction is catalysed by a protic acid
E.g.: H3PO4 or H2SO4
water itself is a weak acid and is unable to duly protonate (provide the H+ electrophile needed to attack the double bond). This is provided by the acid instead
Does the hydration of an alkene follow Markovnikov’s rule?
where necessary
Yes
What is the name of the reverse reaction that forms alkenes from alcohols?
Dehydration
This reaction is catalysed by concentated H2SO4
What is esterification?
This is the reaction of an alkanol and a carboxylic acid to produce an ester and water
What characterises the esterification reaction?
It is a reversible reaction
If nothing is taken out of the reacting system, the backward reaction can occur
What catalyses the esterification reaction?
conc. H2SO4
What is the reverse reaction of esterification called?
Hydrolysis
