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ocr chem > module 4 - core organic chemistry > Flashcards

module 4 - core organic chemistry Flashcards

1
Q

different ways of presenting molecules

A
  • empircal
  • molecular
  • displayed
  • structural
  • general
  • skeletal
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2
Q

general formula of alkanes

A

CnH2n+2

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3
Q

structural formular of butane

A

CH3CH2CH2CH3

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4
Q

displayed formular of ethanol

A

H H
/ /
H—-C———C—O—-H
/ /
H H

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5
Q

skeletal formular of butan-2-ol

A

draw

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6
Q

homologus series

A

organic compounds that have the same functional group but each successive member differs by CH2

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7
Q

functional group

A

group of atoms responsible for characteristic reactions of a compound

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8
Q

example of a functional group

A

COOH

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9
Q

alkyl group general formula

A

CnH2n+1

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10
Q

aliphatic

A

compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings

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11
Q

alicyclic

A

aliphatic compound arranged in non-aromatic rings with or without side chains

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12
Q

aromatic

A

a compound containing a benzene ring

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13
Q

amine displayed formula

A

H
/
-N
\
H

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14
Q

aldehyde molecular formula

A

-CHO

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15
Q

difference between saturated and unsaturated hydrocarbons

A

saturated - single c-c bonds only and saturated with hydrogens

unsaturated - presence of multiple c-c double bonds.

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16
Q

isomerism

A

where molecules exist with the same molecular formula, with a different structural formula

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17
Q

two types of isomerism

A

structural
stereo

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18
Q

3 types of structural isomers

A

position
functional group
chain

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19
Q

how are covalent bonds broken

A

homolytic fission
heterolytic fission

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20
Q

homolytic fission

A

bond splits equally - free radicals formed

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21
Q

heterolytic fission

A

atom receives both electrons from bonding pair

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22
Q

radical

A

species with unpaired electron

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23
Q

curly arrow represents…

A

movement of electron pair, showing either heterolytic fission or formation of a covalent bond

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24
Q

why does the boiling point of alkanes increase as the molecule gets bigger

A
  • more electrons
  • stronger london forces which require more energy to break
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25
Q

what are alkanes

A
  • saturated hydrocarbons containing single c-c and c-h bonds as σ bonds
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26
Q

what are σ bonds

A

end on end overlap of the sp2 orbital

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27
Q

bond angle of alkanes

A

109.5

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28
Q

shape of alkanes

A

tetrahedral shape

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29
Q

which alkane has a higher boiling point : straight chain or branched

A
  • straight chain alkanes have higher boiling points than branched alkanes
  • molecules can get closer making more points of contact for london forces to occur, so more energy is required to break these forces
30
Q

why are reactions of alkanes limited

A

due to lack of polarity of alkane σ bonds

31
Q

what reactions do alkanes go under

A

combustion reactions
free radical substitution

32
Q

reactivity of alkanes

A
  • relatively unreactive
  • non polar
  • very low polarity of σ bonds present
33
Q

uses of alkanes

A

fuels - readily available, easy to transport, burns to release no toxic products

34
Q

incomplete combustion of alkanes can produce …

A

carbon monoxide

35
Q

dangers of carbon monoxide

A
  • colourless, odourless + highly toxic.
  • binds irreversibly with haemoglobin in rbc to form carboxyhaemoglobin preventing oxygen passing round body.
36
Q

three steps of free radical substitution

A

initiation
propagation
termination

37
Q

what are the only two reactants that can react together in a free radical substitution

A

a halogen atom and an alkane

38
Q

reaction of chlorine with methane

A

full reaction:
CH4(g) + Cl2(g) -> CH3Cl(g) + HCl(g)

initiation:
Cl2 —> (UV) 2Cl*

propagation:
CH4 + Cl* -> CH3* + HCl
CH3* + Cl2 -> CH3Cl + Cl*

termination:
2Cl-> Cl2
2CH3 -> C2H6
Cl + CH3* -> CH3Cl

39
Q

reaction of bromine with methane

A

full reaction:
CH4(g) + Br2(g) -> CH3Br(g) + HBr(g)

initiation:
Br2 —> (UV) 2Br*
propagation:
CH4 + Br* -> CH3* + HBr
CH3* + Br2 -> CH3Br + Br*

termination:
2Br-> Br2
2CH3 -> C2H6
Br+ CH3* -> CH3Br

40
Q

limitations of free radical substitutions

A
  • collisions are uncontrollable so can’t make one particular product
  • further substitutions can happen
  • if unwanted product is made, expensive separation will be required
  • reactions at different positions in a carbon chain
41
Q

what are alkenes

A
  • unsaturated hydrocarbons containing c-c double bonds
  • double bond comprised of a σ bond and π bond
42
Q

what is a π bond

A
  • sideways overlap of p orbitals
43
Q

longer chain alkenes =

A

less volatile than shorter chain cause there’s more electrons, more and stronger london forces, requiring more energy to break

44
Q

more branched alkenes =

A

more volatile than less branched - can’t pack closely, less points of contact, less london forces, requires less energy to break

45
Q

explanation of shape of alkenes

A

trigonal planar shape 120
- three bonding pair of electrons are in plane of molecule and repel each other (electron pair repulsion)
- The fourth π bonding pair forms double bond in combination with carbon-carbon σ bond

46
Q

stereoisomerism

A

compounds with the same structural formula but with a different spatial arrangements

47
Q

presence of a double bond can create two possible structures. what are they

A

cis structure
trans structure

48
Q

how does E/Z isomerism occur

A
  • if the C=C double bond is quite rigid and prevents freedom of rotation
  • 2 different atoms or groups on each carbon atom of the double bond
49
Q

when is E/Z naming applied

A

when there are 3/4 different substituents

50
Q

difference between E/Z isomerism and cis/trans isomerism

A

cis/trans isomerism is used when the groups attached to both the carbons are the same
E/Z isomerism is used when there is 3 or 4 different groups are attached to each carbon

51
Q

what is the name of the rule used to identify E/Z stereoisomers

A

cahn-ingold-prelog (cip)

52
Q

cip rules

A
  • atom with the higher atomic number has the higher priority
  • if atoms or groups are the same, next point of connection is considered
53
Q

name of mechanism in which alkenes react

A

electrophilic addition

54
Q

reactivity of alkenes in terms of relatively low bond enthalpy of π bond

A
  • π bond occurs above and below the two nuclei so weaker attraction
  • the π electrons are more exposed than the σ bond so they’re more prone to electrophilic attack
55
Q

4 addition reactions of alkenes

A

hydrogenation
halogenation
hydrohalogenation
hydration

56
Q

addition reaction of hydrogen in presence of a suitable catalyst

A

hydrogenation:
- H2 and Ni catalyst necessary
- 150°C
- alkene -> alkane

57
Q

addition reaction of halogens to form dihaloalkanes, including qualitative test

A

halogenation:
- add bromine water to sample
- presence of alkene = orange -> colourless

58
Q

addition reaction of hydrogen halides to form haloalkanes

A

hydrohalogenation:
-HX has a permanent dipole
- Hδ⁺ is the electrophile
- Pair of e⁻s attracted from π bond
- Heterolytic fission of H-X bond
- Carbocation formed (C⁺)
- X⁻ now a nucleophile
- single halogen atom added to the molecule

59
Q

addition reaction of steam in the presence of an acid catalyst

A

hydration:
- h2o , 300°C
- H3PO4 (catalyst)
- alkene -> alcohol
- industrial prep of alcohol

60
Q

product of hydrogenation

A

alkene -> alkane

61
Q

product of halogenation

A

dihaloalkane

62
Q

product of hydration

A

alcohol

63
Q

electrophile

A

electron pair acceptor
- an atom or group of atoms that is attracted to an electron-rich centre and accepts an electron pair
- usually positive ion or contains atom with partial positive charge (δ⁺)

64
Q

electrophilic addition in alkenes by heterolytic

A

hx has a permanent dipole
- hδ⁺ is the electrophile
- pair of e⁻s attracted from π bond
- heterolytic fission of H-X bond
- carbocation formed (C⁺)
- x⁻ now a nucleophile
- single halogen atom added to the molecule

65
Q

rule that predicts formation of a major organic product

A

markovnikov’s rule

66
Q

markovnikov’s rule

A
  • halide ion will always add to most stable carbocation
  • number of carbon atoms attached to carbocation decides stability
67
Q

more carbons attached to carbocation =

A

more stable

68
Q

conditions needed for polymerisation

A

high pressure, heat and a catalyst

69
Q

benefits and limitations of sustainability of processing waste polymers by combustion for energy production

A
  • combustion removes the polymers and can generate power as an additional benefit - thereby saving fossil fuels.
  • toxic products of some polymers and polymers that contain chlorine would create HCl as a waste gas which contributes to acid rain
  • this process still causes environmental pollution as carbon within polymer can be released as carbon dioxide contributing to global warming
70
Q

benefits of sustainability of processing waste polymers by use as organic feedstock for production of plastics

A
  • chemical feed-stock recycling breaks down polymers without separating them = forms simple gases that can then be used to manufacture pure, fresh polymers
  • waste polymers broken down, by chemical and thermal processes, into monomers, gases and oils
  • products are then used as raw materials in production of new polymers and other organic chemicals
71
Q

limitations of sustainability of processing waste polymers by removal of toxic waste products

A
  • use of landfill sites = not ideal

ocr chem (4 decks)

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