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chemistry > module 4.2 - core organic > Flashcards

module 4.2 - core organic Flashcards

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1
Q

list and describe the three types of alcohol

A

primary - one alkyl group
secondary - two alkyl groups
tertiary - three alkyl groups

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2
Q

how are alcohols classified?

A

by the number of alkyl groups bonded to the hydroxy bearing carbon atom

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3
Q

why are alcohols liquid at room temperature and miscible with water

A

because the intermolecular forces (london dispersion forces) are weak
the OH group is polar and forms hydrogen bonds with water increasing miscibility

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4
Q

explain the trend in boiling points as alcohol chain increases

A

alcohol boiling point increases with chain length because there is the same amount of hydrogen bonding but more london dispersion forces.

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5
Q

do alcohols or their equivalent alkene have the higher boiling point?
why?

A

alcohols have the higher boiling point because alcohols have a hydroxy group which is stronger than the CH bond

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6
Q

alcohol functional groups always have the suffix priority, except from which 3 functional groups?

A

aldehydes - C=O (end of chain)
ketones - C=O (middle of chain)
carboxylic acids - COOH

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7
Q

how is alcohol miscibility affected by chain length

A

miscibility decreases as chain length increases because the ratio of polar: non-polar molecules decreases (more non-polar)

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8
Q

what are the 4 reactions of alcohols

A

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

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9
Q

what do primary alcohols form when oxidised

A

form aldehydes, then carboxylic acids

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10
Q

what do secondary alcohols form when oxidised

A

form ketones + water

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11
Q

what do tertiary alcohols form when oxidised

A

tertiary alcohols resist oxidation

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12
Q

define carbonyl
give examples of carbonyls

A

carbon double bonded to oxygen
aldehydes, ketones and carboxylic acids

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13
Q

define miscibility

A

the ability of liquids to mix with each other

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14
Q

what is required to oxidise alcohols and how

A

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+)

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15
Q

how do you stop a primary alcohol from oxidising from an aldehyde to a carboxylic acid

A

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

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16
Q

how can you favour the production of an aldehyde in the oxidation of primary alcohols

A

by making sure the starting alcohol is in excess and the oxidising agent is limiting

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17
Q

how can you favour the production of a carboxylic acid in the oxidation of a primary alcohol

A

use an excess of oxidising agent
use concentrated sulfuric acid instead of dilute
heat the reaction under reflux

18
Q

what happens when we heat reactions under reflux

A

any volatile products are condensed and returned to the reaction mix

19
Q

how do you separate the products of the oxidation of primary alcohols?

A

distillation
aldehydes have a lower bp than carboxylic acids because carboxylic acids can form hydrogen bonds
separates the carboxylic acid

20
Q

how can you represent one molecule of oxidising agent

A

[O]

21
Q

why can ketones not be further oxidised

A

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

22
Q

why do tertiary alcohols resist oxidation

A

because the carbon bonded to the alcohol group is not directly bonded to any hydrogen atoms
hydrogen atoms need to be removed for oxidation

23
Q

why do we heat oxidation reactions of alcohols under reflux

A

ensures all of the alcohol is oxidised and allows for continued heating without any mixture escaping

24
Q

what is the oxidising agent required to oxidise alcohols

A

K2CrO7/ H2SO4

25
Q

define dehydration reactions

A

any reaction in which a water molecule is removed from the starting material

26
Q

what are the products of the oxidation of propan-2-ol

A

propanone (ketone as secondary alcohol)

27
Q

name the four structural isomers of the alcohol C4H10O and classify them as primary, secondary or tertiary

A

butan-1-ol = primary
butan-2-ol = primary
2-methylpropan-1-ol
2-methylpropan-2-ol

28
Q

what is produced when an alcohol is heated under reflux in the presence of an acid catalyst (H2SO4/ H3PO4)

A

an alkene - a water molecule is removed

29
Q

what type of reaction is the dehydration of alcohols

A

elimination reaction - eliminates the water molecules

30
Q

what is the product of the reaction between haloalkanes and cyanide ions

A

nitriles

31
Q

a reaction between ammonia and a haloalkane produces a positive species. what is the correct term for the positive species

A

an intermediate

32
Q

what conditions are needed for the elimination with a haloalkane

A

heat under reflux

33
Q

what is the name given to the process of the break down of chlorofluorocarbons by light

A

photolysis

34
Q

in what decade were CFCs initially banned

A

1970s

35
Q

what are the 3 stages to the reaction step in synthetic routes

A

carry out reaction
separating desired products
purifying desired products

36
Q

define synthetic route

A

series of reaction steps

37
Q

how can you improve synthetic routes

A

use of solvent - less solvent = reduced possible hazards and wastage

percentage yield and atom economy can be improved by selecting reactions with no by-products and synthetic routes with fewer steps

38
Q

where is the finger print region on the IR spec

A

between 500-1500cm^-1

39
Q

what are 2 uses of the IR spec

A

monitoring of air pollution - eg. carbon monoxide and nitrogen monoxide)
breathalysers - indicate alcohol content of some ones blood

40
Q

how do you determine the mass of a molecule from the IR spec

A

determined from the molecular ion peak - furthest right

41
Q

how do you determine if alcohols are primary or secondary

A

fehling’s solution
warming with acidified potassium dichromate

42
Q

how do you test for carboxylic acids

A

limewater + sodium dichromate

chemistry (9 decks)

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