module 4.2 - core organic Flashcards
list and describe the three types of alcohol
primary - one alkyl group
secondary - two alkyl groups
tertiary - three alkyl groups
how are alcohols classified?
by the number of alkyl groups bonded to the hydroxy bearing carbon atom
why are alcohols liquid at room temperature and miscible with water
because the intermolecular forces (london dispersion forces) are weak
the OH group is polar and forms hydrogen bonds with water increasing miscibility
explain the trend in boiling points as alcohol chain increases
alcohol boiling point increases with chain length because there is the same amount of hydrogen bonding but more london dispersion forces.
do alcohols or their equivalent alkene have the higher boiling point?
why?
alcohols have the higher boiling point because alcohols have a hydroxy group which is stronger than the CH bond
alcohol functional groups always have the suffix priority, except from which 3 functional groups?
aldehydes - C=O (end of chain)
ketones - C=O (middle of chain)
carboxylic acids - COOH
how is alcohol miscibility affected by chain length
miscibility decreases as chain length increases because the ratio of polar: non-polar molecules decreases (more non-polar)
what are the 4 reactions of alcohols
oxidation - loss of a hydrogen
combustion - addition of oxygen to form carbon dioxide/monoxide + water
dehydration/ elimination - water molecule removed
substitution - when a hydrogen halide reacts to form haloalkanes
what do primary alcohols form when oxidised
form aldehydes, then carboxylic acids
what do secondary alcohols form when oxidised
form ketones + water
what do tertiary alcohols form when oxidised
tertiary alcohols resist oxidation
define carbonyl
give examples of carbonyls
carbon double bonded to oxygen
aldehydes, ketones and carboxylic acids
define miscibility
the ability of liquids to mix with each other
what is required to oxidise alcohols and how
an oxidising agent such as acidified potassium dichromate (VI) ions (H+/K2Cr2O7 ^2-)
during the reaction, the orange dichromate ions are reduced to form green Cr3+ ions
(Cr6+ -> Cr3+)
how do you stop a primary alcohol from oxidising from an aldehyde to a carboxylic acid
you remove the aldehyde by distillation
distillation works because aldehydes have a lower boiling point as they cannot form hydrogen bonds
gently heat the alcohol and oxidising agent - produce aldehyde
aldehyde evaporates and passes into the condenser where it forms a liquid again and is removed
how can you favour the production of an aldehyde in the oxidation of primary alcohols
by making sure the starting alcohol is in excess and the oxidising agent is limiting
how can you favour the production of a carboxylic acid in the oxidation of a primary alcohol
use an excess of oxidising agent
use concentrated sulfuric acid instead of dilute
heat the reaction under reflux
what happens when we heat reactions under reflux
any volatile products are condensed and returned to the reaction mix
how do you separate the products of the oxidation of primary alcohols?
distillation
aldehydes have a lower bp than carboxylic acids because carboxylic acids can form hydrogen bonds
separates the carboxylic acid
how can you represent one molecule of oxidising agent
[O]
why can ketones not be further oxidised
because to oxidise we have to remove a hydrogen from the carbon bonded to the oxygen
in a ketone, the carbon is bonded to two other carbons and double bonded to the oxygen so there are no hydrogens to remove
why do tertiary alcohols resist oxidation
because the carbon bonded to the alcohol group is not directly bonded to any hydrogen atoms
hydrogen atoms need to be removed for oxidation
why do we heat oxidation reactions of alcohols under reflux
ensures all of the alcohol is oxidised and allows for continued heating without any mixture escaping
what is the oxidising agent required to oxidise alcohols
K2CrO7/ H2SO4
