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A-Level Chemistry > 11-12 Organic Chemistry > Flashcards

11-12 Organic Chemistry Flashcards

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1
Q

What is a sigma bond?

A

Def: Atom orbitals overlap directly between the bonding atoms
- Each overlapping orbital contains one electron, so the sigma bond contains two electrons shared
- 4 sigma bonds

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2
Q

How would you sketch a sigma bond/electron density of a sigma bond?

A

C 0 C (oval)

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3
Q

What is the shape around a carbon atom and why?

A

Tetrahedral with 109.5 angles
- 4 bonding pairs (4 sigma bonds)
- Repel as far apart as possible
- Saturated hydrocarbons are always tetrahedral

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4
Q

Why are the 3D shapes of alkanes constantly changing?

A

The molecules can rotate freely about the sigma bonds

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5
Q

Why do alkanes have different boiling points?

A

As molecules increase in length:
- There are more electrons
- Greater surface contact between molecules (as molecules have a larger surface area)
- More and stronger London forces
- More energy required to overcome the forces

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6
Q

Why do only London forces act between molecules?

A

Non-polar so only London forces

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7
Q

What is the trend with boiling point and branching and why?

A

More branching = Lower boiling point
- Less surface contact is possible
- Weaker and/or fewer London forces
- Less energy required to overcome them

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8
Q

Why do you need to compare isomers when comparing boiling points?

A

Same number of electrons - branching is the only factor changing

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9
Q

Why do alkanes have low reactivity?

A
  • C-C and C-H sigma bonds are strong
  • C-C bonds are non polar
  • C and H re so similar in electronegativity that C-H bonds are effectively non-polar
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10
Q

What are the advantages from using alkanes as fuels?

A
  • Give out lots of energy
  • Readily available
  • Easy to transport
  • When burned in plenty of oxygen, no toxic products are formed
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11
Q

What is produced in complete combustion of alkanes?

A

Carbon dioxide and water

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12
Q

How much extra oxygen is needed for complete combustion as you descend the homologous series?

A

1 1/2 O2

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13
Q

What are alkanes useful for?

A

Fuels - main components of natural gas and crude oil
Very stable

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14
Q

What is formed during incomplete combustion (limited supply of oxygen)?

A

Carbon monoxide (CO) and Carbon (C)

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15
Q

How do alkanes react with halogens?

A

UV radiation in sunlight provide initial energy for a reaction to take place
CH4 (g) + Br2 (l) –> CH3Br(g) + HBr (g)
Substitution reaction (hydrogen atom has been substituted by a halogen atom)

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16
Q

What is radical substitution?

A

Mechanism for the bromination of methane

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17
Q

What are the 3 stages of radical substitution?

A

Initiation
Propagation
Termination

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18
Q

Why is carbon so special?

A
  • Four electrons in outer shell
  • Form four covalent bonds
  • Single, double, and triple bonds
  • Strong bonds to itself, chains and rings of carbon atoms
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19
Q

What does a saturated hydrocarbon mean?

A

Single bonds only

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20
Q

What does an unsaturated hydrocarbon mean?

A

Contains carbon-to-carbon multiple bonds

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21
Q

What is a homologous series?

A

A series of compounds with similar chemical properties whose successive members differ by addition of a -CH2- group

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22
Q

What is the functional group responsible for?

A

The molecule’s chemical properties

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23
Q

Define aliphatic

A

Chains (unbranded or branched) or non-aromatic rings

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24
Q

Define alicyclic

A

Joined in unbranched or branched rings (not benzene ring)

25
Q

Define aromatic

A

Soem or all carbon atoms are in a benzene ring

26
Q

What are the 3 homologous series of aliphatic hydrocarbons?

A

Alkanes - single bonds
Alkenes - double C-C
Alkynes - triple C-C

27
Q

How do you name an aliphatic alkane?

A
  1. Suffix - ane
  2. Longest chain of carbon atoms
  3. Side chains (alkyl groups)
  4. Numbers to show position of alkyl groups
  • Ordered alphabetically
28
Q

What if there are 2 chains with the same length?

A

The most branches is the longest chain

29
Q

How do you name alicyclic alkane?

A
  • Cycloalkane
  • Prefix: cyclo
30
Q

How do you name alkenes?

A

Same rules but suffix is -ene
Indicate position of double bond

31
Q

What is the alkene functional group and suffix?

A

C=C
-ene

32
Q

Haloalkane functional group
(R is any alkyl group) and prefix

A

R-X
- Cl -Br -I
X = Cl, Br, I
chloro-, bromo-, iodo-

33
Q

Alcohol functional group
(R is any alkyl group) and suffix/prefix

A

-OH
- hydroxy
-ol

34
Q

Aldehyde functional group
and suffix

A

C
||
C
/ \
R H
-al
-CHO

(Do not need numbers as group always on 1)

35
Q

Ketone functional group and suffix

A

O
||
C
/ \
R R
-one
-C(CO)C-

36
Q

Carboxylic acid functional group + suffix

A

O
||
C
/ \
R OH
-oic acid
-COOH

37
Q

Ester functional group and suffix

A

-COOC-
-oate

38
Q

Acyl chloride functional group and suffix

A

-COCl-
-oyl chloride

39
Q

Amine functional group, prefix and suffix

A

-NH2
amino-
-amine

40
Q

Nitrile functional group and suffix

A

-CN
-nitrile

41
Q

What is the molecular formula?

A

Number and type of atoms of each element present in a molecule

42
Q

What is the empirical formula?

A

Simplest whole-number ratio of the atoms of each element present in a compound

43
Q

What is the general formula?

A

Simplest algebraic formula for any member of a homologous series

44
Q

What are the general formulas of:
Alkanes
Alkenes
Alcohols
Carboxylic acids
Ketones

A

CnH2n+2
CnH2n
CnH2n+1OH
CnH2nO2
CnH2nO

45
Q

What is the displayed formula?

A

Shows the relative positioning of all the atoms in a molecule and the bonds between them

46
Q

What is structural formula?

A

Smallest amount of detail necessary to unambiguously show the arrangement of the atoms in a molecule
Shows which groups are bonded together

47
Q

What are the rules of skeletal formula?

A
  • A line represents a single bond
  • An intersection of two lines represents a carbon atom
  • The end of a line represents a -CH3 group
  • Show functional groups (e.g. halogen)
48
Q

What is a structural isomer?

A

Compounds with the same molecular formula but different structural formulae

49
Q

What is homolytic fission?

A

One electron goes to each atoms (electrons split)
Form reactive radicals (atoms or groups of atoms with unpaired electrons)

50
Q

What is heterloytic fission?

A

Both electrons go to one atom
Results in ions

51
Q

What is does a curly arrow represent?

A

The movement of electron pairs when bonds are being broken or made

52
Q

What happens in an addition reaction?

A

Two reactants join together to form one product
A molecule is added to an unsaturated compound, breaking the double bond and forming a single saturated compound

53
Q

What happens in a substitution reaction?

A

An atom or group of atoms is replaced by a different atom or group of atoms

54
Q

What is an elimination reaction?

A

Opposite of addition
A small molecule is removed from a larger one
One compound forms two, one of which is unsaturated

55
Q

What happens in each stage of radical substitution?

A

Initiation:
Homolytic fission
Stable molecule –> 2 radicals

Propagation:
2 propagation steps, chain reaction
1 radical + 1 stable molecule –> 1 radical + 1 stable molecule

Termination
Both radicals removed from the reaction mixture, stopping the reaction
2 radicals –> 1 stable molecule

56
Q

Give the radical substitution stages for methane and bromine

A

1 Initiation:
Br2 –> Br* + Br*

2 Propagation
Br* + CH4 –> HBr + CH3*

3 Termination
Br* + Br* –> Br2
CH3* + Br* –> CH3Br
CH3* + CH3* –> C2H6

57
Q

How do you get the overall equation for the reaction?

A

Cancel out the radicals of the propagation steps

58
Q

What is multiple substitution and use the bromine and methane reaction as an example?

A

The CH3Br produced can asp react with a bromine radical and a further hydrogen atom is substituted

    \+Br2 CH4 --> CH3Br---->CH2Br2...
    -HBr

A-Level Chemistry (15 decks)

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