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Advanced Higher Chemistry > Last Minute Cram - Organic > Flashcards

Last Minute Cram - Organic Flashcards

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1
Q

when atomic orbitals overlap…

A

they combine to form molecular orbitals

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2
Q

why is a hydrogen molecule more stable than hydrogen atoms

A

bonding molecular orbital has lower energy than the seperate atomic orbitals

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3
Q

overlap of two hydrogen atomic orbitals

A

the formation of a σ bond

more stable

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4
Q

σ bonds

A

covalent bonds formed between atoms when end-on overlap of orbitals occurs

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5
Q

How can bonding in hydrocarbons be explained?

A

using hybridisation

2s and 2p orbitals combine to form four degenerate orbitals

hybrid formed from 1 s orbital and 3 p orbitals is called sp3

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6
Q

sp3 orbitals in hydrocarbons

A

all half filled with the electron far more likely to be found in the larger lobe

(shape is like sideways bowling pin)

electrons repel so the 4 sp3 orbitals surrounding the carbon will form a tetrahedral shape max angle 109.5 degrees

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7
Q

alkanes (hybridisation)

A

carbon to carbon single bonds in alkanes result from overlapping sp3 orbitals forming σ bonds
4 σ bonds in methane
7 σ bonds in ethane

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8
Q

free rotation of orbitals in alkanes

A

σ bonds must be lying along the line joining both atoms so there will be free rotation around these orbtials.

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9
Q

alkenes (hybridisation)

A

one electron from 2s shell is promoted to empty 2p orbital

this results in three hybrid orbitals and one remaining unhybridised 2p orbital

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10
Q

sp2 orbitals

A

formed from one s orbital and 2 p orbitals

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11
Q

sp2 orbitals in alkenes

A

repel each other resulting in bond angle of 120 degrees between them

overlap to form σ bonds

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12
Q

orbitlas in a molecule of ethene

A

σ bonds
unhybridised p orbitals perpendicular to the plane of the molecule
p orbitals of carbon parallel and close enough to overlap sideways

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13
Q

π molecular orbitals

A

covalent bond formed by the sideways overlap of two parallel atomic orbitals

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14
Q

hybridisation summary alkanes

A 
longer C-C bond
free rotation
tetrahedral
sp3 hybridisation
all σ
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15
Q

hybridisation summary alkenes

A 
short C=C bonds 
**bonds NOT twice as strong**
planar
no rotation
sp2 hybridisation
σ  and π
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16
Q

hybridisation summary alkynes

A

sp hybridised
bond angles of 180
σ and π

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17
Q

comparing σ and π

A

double bonds are stronger but not twice as strong

this is because sideways overlap is weaker than end-on overlap

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18
Q

hybridisation in benzene

A

sp2

each C has 3 filled sp2 orbitals
1 makes a sigma bond with H and other two make sigma bonds with neighbouring 2 Cs

this leaves an electron occupying a p-orbital on each of the carbons

each p orbital overlaps side on creating a pi bond above and below the plane of the molecule

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19
Q

orbitial diagram of increasing energy

A

top

pi anti-bonding
sigma anti-bonding
non-bonding (contains lone pairs)
pi bonding
sigma bonding

bottom

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20
Q

what compounds are colourless

A

organic compounds that only contain sigma bonds

HOMO is sigma bonding orbital
LUMO is sigma anti-bonding orbital

energy gap to promote an electron is very large
these absorptions correspond to UV part of the specturm

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21
Q

excitations of electrons in compounds containing simple pi bonds

A

still involve large transition from HOMO (pi bonding) to LUMO (sigma anti-bonding)
still absorb in UV region

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22
Q

conjugated systems

A

prganic molecules that are coloured contain delocalised electrons within alternating carbon to carbon single and double bonds

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23
Q

the greater the number of atoms spanned by the delocalised electrons…

A

the smaller the energy gap will be between the delocalised orbital and the next unoccupied orbital

will require less energy to excite electrons (coloured)

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24
Q

chromophores

A

group of atoms within a molecule that is responsible for its colour

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25
Q

why do coloured compounds arise?

A

visible light is absorbed by the delocalised electrons in the chromophore which are then promoted to a higher energy molecular orbital

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26
Q

if the chromophore absorbs light of one colour..

A

the complementary colour is observed

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27
Q

greater degree of conjugation…

A

smaller energy gap
less energy required
appear orange or red

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28
Q

what can stereoisomerism be split into?

A

geometric isomerism

optical isomerism

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29
Q

structural isomerism

A

organic compounds which have the same molecular formula but different structural formula

have different physical and chemical properties and can belong to different homologous series

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30
Q

stereoisomerism

A

arises whenever there is more than one way to organise a given number of atoms
molecules have the same molecular and structural formula

have a different three-dimensional arrangement in space which makes them non-superimposable

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31
Q

geometric isomerism - cis

A

both groups are on the same side of the double bond

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32
Q

geometric isomerism - trans

A

the groups are on opposite sides of the double bond

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33
Q

naming cis and trans moleules

A

same systematic name as before but add cis or trans at start of name

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34
Q

physical properties of geometric isomers

A

trans isomer - closer packing in the solid state
increase in London dispersion forces
increases mp

eg: in C-Cl bonds are polar
trans - polarities cacel out and overall non-polar

cis - extra pdp.pdp interactions between molecules gives a higher bp

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35
Q

major kinds of fats in food

A

saturated
polyunsaturated
monounsaturated
trans fatty acids

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36
Q

what fats raise blood cholesterol

A

saturated and trans

risk of coronary heart disease which leads to heart attack and increased risk of stroke

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37
Q

unsaturated fats (oils)

A

kinks in hydrocarbon which makes close packing more difficult
ldf weaker
lower mp

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38
Q

triglycerides

A

made from tans unsaturated fatty acids

pack together closely
ldf stronger
higher mp

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39
Q

aromatics

A

organic molecules containing a benzene ring

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40
Q

benzene ring

A

3 valence electrons form sigma bonds
fourth delocalised over entire ring

six sp2 orbitals

planar molecule with the unfilled p orbital above and below

2p orbitals combine to form a set of delocalised pi molecular orbitlas

C6H6

41
Q

why does benzene resist bromine addition reaction?

A

does not have C=C double dins
does not discolour bromine solution
does not undergo addition reactions

42
Q

substituted benzene ring

A

phenyl group

C6H5

43
Q

reactions of benzene

1. with bromine or chlorine

A

requires a catalyst
eg: aluminium chloride or iron(III) bromide

catalyst polarises bromine molecule

partially +ve bromine can then attack one of the C on benzene

creates carbonation which is stabilised by delocalisation on the ring

44
Q

reactions of benzene

2. nitration

A

heat HNO3 or H2SO4 under reflux

electrophilic substitution by nitronium cation NO2+

45
Q

reactions of benzene

3. sulfonation

A

heat under reflux for several hours with conc. H2SO4

used in manufacture of detergents

46
Q

reactions of benzene

4. alkylation

A

halogenoalkane and ALCl3 catalyst

ACl3 increases polarity of C-halogen
partially positive R group attacks benzene ring

some halogenoalkanes can form a carbocation

47
Q

what is a drug?

A

natural or synthetic substances which affect the biochemical systems in the body

48
Q

what is a medicine?

A

a drug that has a beneficial effect on the body

normally contains one or more drugs amongst other ingredients

49
Q

hwo a medicine functions

A

most drugs work by binding to a receptor (usually protein)

effective medicines work by binding to the receptor site
either mimic response of active molecule or block the effect of an active molecule

this is reversible and involves weak forces i.e. H bonding

50
Q

lock and key analogy

A

key=molecule

lock=receptor

51
Q

agonist

A

medicine that interacts with a receptor to produce a response similar to the body’s natural active compound

in analogy: a good copy of the original key. Will fit into lock and will turn

52
Q

antagonist

A

interacts with a receptor to produce no response because it prevents the action of the body’s natural active compound

stops cell activity and prevents other substances occupying receptor

analogy: badly copied key that fits into lock but wont turn

53
Q

pharmacophore

A

minimum structural feature that gives pharmacological activity

shape compliments receptor site

54
Q

designing a drug

A

needs to be absrobed in blood stream, reach target efficiently, stable enough to survive journey and be eliminated in a sensible timeframe.

55
Q

functional groups involved in drug-receptor sites

A

generally contained in amino acids

56
Q

enantiomers

A

substances which show optical isomerism

57
Q

R-form

A

if a solution of one enantiomer rotates the plane of polarised light in a clockwise direction it is known as the R-form

58
Q

S-form

A

if a solution of the other enantiomer rotates the plane of polarised light in an anti-clockwise direction it is known as the S-form

59
Q

if the solutions are equally concentrated…

A

the amount of rotation caused by the two isomers is exactly the same but in opposite directions

60
Q

racemic mixture

A

50/50 mixture of the two enantiomers in equal concentrations

optically inactive and has no effect on plane polarised light

61
Q

chiral carbon

A

contains four different groups

62
Q

a mass spectrometer does 3 things:

A
  1. vapourises a minute sample of compound
  2. ionises the vaporised molecules
  3. separates and analyses the ions produced when the molecules fall apart according to their mass/cahrge ratio

this gives a mass spectrum

63
Q

how is a radical cation formed?

A

a high-energy electron can dislodge an electron from a bond, creating a radical cation
(+ve ion with an unpaired electron)

fragmentation then occurs

64
Q

m or m/z

A

mass or mass to charge ratio

x-axis on mass spectrum

65
Q

main use of mass spectrum

A

identify the molecular ion (biggest one)

66
Q

table used in empirical formula

A

mass
gfm
moles
divide by smallest

67
Q

empirical formula

A

XnYmZr

simplest ratio

68
Q

what does infrared cause?

A

molecules to vibrate

different bonds vibrate differently

69
Q

explain the effect infrared radiation has on the bonds within molecules and how this allows different functional groups to be identified

A

infrared causes molecules to vibrate. Different bonds absorb at different wavenumber so they can be identified

70
Q

the greater the mass of the atoms…

A

the lower the frequency of vibrations

71
Q

the stonger the bond…

A

the higher the frequency of vibrations

72
Q

fingerprint region

A

area of the spectrum below 1500cm^-1

it has very complicated series of absorptions due to lots of different bonding vibrations within the molecule

73
Q

what nuclei have nuclear spin?

A

odd mass or odd atomic number

74
Q

magnetic field of nucleus

A

since the nucleus is a charged particle in motion, its will develop a magnetic field

75
Q

when a magnetic field is applied the nuclei…

A

line up parallel to the applied field, either spin aligned or spin opposed

76
Q

nuclei aligned opposed to magnetic field

A

high energy state

77
Q

nuclei aligned with magnetic field

A

low energy state

78
Q

as nuclei relax back to low-energy alignment, energy in the radio wave frequency is released…

A

this energy is detected and recorded as peaks on a spectrum

79
Q

absolute values are difficult to obtain so

A

values often obtained by refernce to a standard assigned with delta value 0
values mearued in the ppm

80
Q

standard used in NMR

A

tetramethylsilane (TMS)

has an NMR signal well away from those found in most organic molecules

81
Q

protons emitting radiation of the same frequency are said to be…

A

in the same proton environment

82
Q

NMR

the area under the peak gives information about

A

how many protons are in each environment

83
Q

High resolution NMR

A

run using a higher radio frequency and the peaks have more detail

84
Q

n+1 rule

A

the number of peaks in a multiplet can give additional information about the structure

n is the number or hydrogen atoms attached to the adjacent carbon

85
Q

plotting on an nmr spectra

A

chemical shift ppm found in d.b.

how high the line goes up depends on how many of the same proton environment

86
Q

amines

A

organic compounds based on ammonia
functional group -NH2
one or more H atoms replaced by alkyl groups or aryl groups (based on benzene)

87
Q

classification of amines

A

similar to alcohols

primary - one R group and 2 H atoms

sec. - 2 R groups and 1 H
tert. - 3 R groups

R groups can be the same or different

88
Q

naming amines (basic)

A

add suffix -amine to the name of the R group

eg: ethylamine

89
Q

naming amines with multiple groups

A

prefix amino is used

eg: 2-aminopropanoic acid

groups named alphabetically

eg: butyldimethylamine

90
Q

amines and intermolecular forces

A

primary and secondary have N-H bond i.e. hydrogen bonding

tertiary amines have no H atoms so no H bonding

91
Q

amines boiling points

A

tertiary amines lower due to lack of H bodning

92
Q

solubility of amines

A

H bonding between amine and water

solubility decreases as the number of carbon atoms increases

93
Q

reaction of amines

A

amines can accept protons from water or an acid

since amines are bases they react with acids in neutralisation reactions

94
Q

what is gravimetric analysis

A

a quantitative determination of an analyte based on the mass of a solid

95
Q

the mass of the analyte present in a substance is determined by

A

changing that chemical substance into a solid by precipitation, with an appropriate reagent, of known chemical composition and formula

96
Q

heating to a constant mass

A

final product has to be dried completely

heating substance in a crucible with the blue frame of a bunsen burner, allowing it to cool in a desiccator and then reweighing

repeat until constant mass obtained

HEAT
DRY
WEIGH
REPEAT

97
Q

weighing by difference

A

mass of crucible is measured before adding substance

final mass of substance determined by subtracting mass of crucible from the mass of crucible and dried substance

98
Q

steps in gravimetric analysis calculation

A

use mass of empty cruicible and cruicuble+ substance to work out mass of hydrated substance

same with anhydrous substance

mass of water removed

moles of water removed

moles of substance

ratio of moles

needs to be whole number

Advanced Higher Chemistry (12 decks)

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