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Chemistry A Level > Hydrocarbons and Basic Organic Concepts > Flashcards

Hydrocarbons and Basic Organic Concepts Flashcards

1
Q

What is a saturated hydrocarbon?

A

A hydrocarbon where only single bonds exist between carbon atoms

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2
Q

What is an unsaturated hydrocarbon?

A

A hydrocarbon where one or more carbon-carbon double or triple bonds are present

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3
Q

Are alkanes unsaturated or saturated?

A

Saturated, only single bonds are present between carbon atoms

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4
Q

Are alkenes saturated or unsaturated?

A

Unsaturated, there is a carbon-carbon double bond present in all alkenes

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5
Q

What is a homologous series?

A

A series of molecules that have the same general formula and neighbouring molecules differ by CH2

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6
Q

What is a functional group?

A

A group of atoms responsible for characteristic reactions of a compound

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7
Q

What is the general formula for alcohols?

A

CnH2n+1OH

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8
Q

What are isomers?

A

Organic compounds that have the same molecular formula but different displayed and structural formula

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9
Q

What are stereoisomers?

A

Compounds with the same molecular and structural formula but differ only in the spatial arrangement of their atoms

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10
Q

What is a Z stereoisomer?

A

A stereoisomer where the highest priority groups are on the same side of the carbon=carbon double bond

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11
Q

What is an E stereoisomer?

A

A stereoisomer where the highest priority groups are on different sides of the carbon=carbon double bond

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12
Q

What is a cis-isomer?

A

An isomer where the side chains are on the same side of the carbon=carbon double bond

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13
Q

What is a trans-isomer?

A

An isomer where the side chains are on opposite sides of the carbon=carbon double bond

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14
Q

What is a hydrocarbon?

A

A compound containing carbon and hydrogen only

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15
Q

What is an aliphatic hydrocarbon?

A

A compound containing straight or branched chains

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16
Q

What is an alicyclic compound?

A

A compound containing a ring structure

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17
Q

What is an aromatic compound?

A

A compound containing benzene (C6H6)

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18
Q

What is a polar substance?

A

A substance where the elements making up a substance/compound have a difference in electronegativity electrons lie closer to the more electronegative element

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19
Q

What is a substitution reaction?

A

A reaction in which an atom or group of atoms on the organic molecule is directly replaced by another

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20
Q

What is a free radical?

A

Very reactive species containing an unpaired electron

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21
Q

What are the stages of free radical substitution reactions?

A
  • Initiation
  • Propagation
  • Termination
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22
Q

What happens in initiation?

A

Free radicals are generated

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23
Q

What happens in propagation?

A

Free radical reacts with a molecule to produce another free radical

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24
Q

What happens in termination?

A

Two free radicals react to form a normal molecule

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25
Q

What is homolytic fission?

A

The breaking of a covalent bond with one of the electrons going to each atom, forming two free radicals

26
Q

What is an electrophile?

A

An electron pair acceptor

27
Q

What is hydrogenation?

A

Where gaseous hydrogen is mixed with an alkene at a temperature of 150ºC in the presence of a nickel catalyst, the alkene is saturated and an alkane is produced

28
Q

What is Markonikov’s rule?

A

When a hydrogen halide is added to an unsymmetrical alkene, the hydrogen atoms is added to the carbon with the with the greater number of hydrogen atoms. This is because the carbocation intermediate is more stable in the major product than the minor product

29
Q

What is the major product?

A

The hydrogen joins onto the carbon with the most hydrogens attached to it. The other molecule (eg.bromine) joins to the other carbon. The major product is favoured because the intermediate carbocation is more stable than that of the minor product as carbocations with the most alkyl groups attached are the most stable

30
Q

What is the minor product?

A

The hydrogen joins onto the carbon with the least hydrogens attached to it. The other molecule (eg.bromine) joins to the other carbon

31
Q

When are molecules non-polar?

A

When the electron pair is evenly distributed between the two atoms that the bond is between. Molecules are non-polar when both atoms are approximately equal in electronegativity

32
Q

When are molecules polar?

A

When the atoms that the bond is formed between have different electronegativity, this causes the bond pair of electrons to be distributed unevenly as they’re attracted to the more electronegative atom. The atom that the electrons are closer to has a slightly negative charge and the atom that is further away from the electron pair has a slightly positive charge. The uneven distribution of electrons across the molecule means the molecule is described as having as an overall dipole

33
Q

How can molecules have atoms with different electronegativities but not have a dipole moment?

A

The bonds can be arranged symmetrically so the dipoles on each bond cancel each other out

34
Q

What are dipole-dipole interactions?

A

Polar molecules such as HCl have permanent dipoles due to the much greater electronegatively of the chlorine atom. This means that the oppositely charged ends of the molecule are attracted to each other. This is called a permanent dipole-dipole interaction

35
Q

What are London forces?

A
  • Electrons are randomly moving within the electron shells of a molecule, this can cause electron density to be spread unevenly causing an instantaneous dipole
  • If a second molecule approaches, a small induced dipole occurs, causing a weak attraction between the two molecules
36
Q

What happens to boiling point of noble gases as you go down the group?

A

The boiling point increases because as you go down the group each element has more electrons so the strength of the London forces increases, this means that more energy has to be supplied to overcome the London forces and allow the substance to boil

37
Q

How is a sigma bond formed?

A

2 orbitals approach head on and the orbitals overlap to from a sigma bond, this gives an increased electron density between nuclei

38
Q

How is a pi bond formed?

A

2 p-orbitals approach sideways on, p-orbitals overlap to from a pi bond, increased electron density above and below plane of molecule

39
Q

What is a pi bond?

A

A region of space occupied by a bond pair of electrons, above and below the plane of the molecule, formed by sideways overlap of p-orbitals

40
Q

What determines which groups are the highest priority?

A

The groups with the highest mass are described as being the highest priority

41
Q

When the two highest priority groups are on the same side is it an E or Z isomer?

A

Z, on z zame zide

42
Q

When the highest priority groups are on opposite sides, is it an E or Z isomer?

A

E, for enemies

43
Q

Is a trans isomer the same as an E or Z isomer?

A

E, Z is the same as a Cis isomer (highest priority groups must be the same)

44
Q

Is a pi bond weaker or stronger than a sigma bond?

A

Weaker, the regions occupied by the electron pairs are further away from the nucleus meaning there is a weaker nuclear attraction experienced by the electron pairs and therefore the bond is weaker

45
Q

What does a double bond consist of?

A

A sigma and a pi bond

46
Q

How does the size of a molecule affect it’s boiling and melting points?

A

Longer carbon chains have more London forces because they have more electrons. The electron density of the larger electron clouds fluctuate more readily meaning the London forces are stronger in magnitude, this means that more energy is required to break the London forces so the molecule has a higher melting point

47
Q

How does the branching of a molecule affect its boiling point?

A

The more branched a molecule is, the lower its boiling point. This is because the branches get in the way of surface area interactions between molecules. This means that less energy is needed to break the London forces s the molecule has a lower boiling point

48
Q

What is a structural isomer?

A

An isomer with the same molecular formula but a different structural formula and displayed formula

49
Q

What is homolytic fission?

A

When the electrons from a bond pair each go to a different atom in the bond. Species formed are called radicals and they are written with a dot next to them which represents an unpaired electron

50
Q

What is heterolytic fission?

A

When both electrons from a bond pair go to one of the atoms in the bond, this forms a positive and negative ion, the electrons go to the negative ion

51
Q

How is a covalent bond broken?

A

By homolytic or heterolytic fission

52
Q

What is the general formula for an alkene and alkane?

A
  • Alkene, CnH2n

- Alkane, CnH2n+2

53
Q

Write the free radical substitution equations for the reactions between bromine and ethane

A
  • Initiation, Br2 → 2Br.
  • Propagation, C2H6 + Br. → C2H5. + HBr
  • C2H5. + Br2 → C2H5Br + Br.
  • Termination, C2H5. + Br. → C2H5Br
  • C2H5. +C2H5. → C4H10
  • Br. + Br. → Br2
54
Q

Explain the steps of free radical substitution

A

Initiation- homolytic fission of bromine to form free radicals using UV light

  • Propagation - where one radical reacts and another is formed, this happens twice
  • Termination, where two free radicals react with each other and form a stable product, there are usually 3 possible termination steps
55
Q

What is homolytic fission?

A

Where a covalent bond breaks and each electron goes to a different bonded atom, this generates two radicals

56
Q

What is heterolytic fission?

A

Where a covalent bond breaks and both electrons go to the same bonded atom forming a cation and an anion

57
Q

What is the trend in boiling points of alkanes as the length of the carbon chain increases?

A

As the length of the carbon chain increases, its relative molecular mass increases. Larger molecules have more surface area contacts with adjacent molecules, this increases the number of London forces and therefore more energy is required to overcome these forces meaning boiling point increases as the length of the carbon chain length increases

58
Q

How does branching affect boiling point?

A

The more branched a compound is, the less neatly molecules can fit together meaning there are less surface area contacts between molecules and therefore less London forces between molecules meaning that less energy is required to overcome these forces and therefore boiling point decreases as a molecule becomes more branched

59
Q

What are the possible products of incomplete combustion?

A

CO2, CO, C and H2O is always a product

60
Q

What is the mechanism to form chloromethane from methane?

A

Initiation - Cl2 → 2Cl.
Propagation - CH4 + Cl. → CH3. + HCl
- CH3. + Cl2 → CH3Cl + Cl.
Termination - Cl. + Cl. → Cl2
- CH3. + Cl. → CH3Cl
- CH3. + CH3. → C2H6

61
Q

What is the most stable out of a primary secondary and tertiary carbocation?

A

Tertiary, primary is the least stable

Chemistry A Level (15 decks)

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