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Chemistry > Topic 10 & 20 - Organic chemistry > Flashcards

Topic 10 & 20 - Organic chemistry Flashcards

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1
Q

WWhat are the features of a homologous series?

A
  1. Same general formula
  2. Neighbouring members differ by CH2
  3. Similar chemical properties
  4. Gradation in physical properties
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2
Q

What kind of a trend is there in the boiling points of a homologous series?

A

The boiling point increases with the number of -CH2 groups

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3
Q

Distinguish between empirical, molecular and structural formulas

A

An empirical formula shows the simplest whole number ratio of the atoms it contains

A molecular formula shows the actual number of atoms of each element present

A structural formula is one that shows unambiguously how the atoms are arranged together

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4
Q

What are the three types of structural formulas?

A

A full structural formula shows every atom and bond in the compond

A condensed structural formula can omit bonds between atoms and can swho identical groups bracketed together for simplicity

A stereochemical formula attemps to show the relative positions of atoms and groups in three dimensions

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5
Q

What are structural isomers?

A

Compounds with the same molecular formula with different arrangement of atoms

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6
Q

What is the structural formula of an amine group and what is the suffix name of it?

A

–NH2

–anamine

Primary, secondary, and tertiary amine, respectively:

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7
Q

What is the structural formula of an amide group and what is the suffix name of it?

A

–CONH2

–anamide

Primary amide:

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8
Q

What is the structural formula of an ester group and what is the suffix name of it?

A

–COOC–

–anoate

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9
Q

What is the structural formula of a nitrile group and what is the suffix name of it?

A

–CN

–ananetrile

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10
Q

What is the structural formula of a ketone group and what is the suffix name of it?

A

–C–COC–

–anone

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11
Q

What is the structural formula of an aldehyde group and what is the suffix name of it?

A

–CHO

–anal

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12
Q

What is the structural formula of an alcohol group and what is the suffix name of it?

A

–OH

–anol

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13
Q

What is the structural formula of an a carboxylic acid group and what is the suffix name of it?

A

–COOH

–anoic acid

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14
Q

What is the difference between a *primary, secondary, *and tertiary atom?

A

A primary atom is attached to only one other carbon

A secondary atom is attached to two carbon atoms

A tertiary atom is attached to three carbon atoms

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15
Q

What is the order of volatility of alcohols, halogenoalkanes, carboxylic acids, ketones, alkanes, and aldehydes?

A

From least volatile to most volatile:

carboxylic acid < alcohol < ketone < aldehyde < halogenoalkane < alkane

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16
Q

Desribe the solubility in water of alcohols, halogenoalkanes, carboxylic acids, ketones, alkanes, and aldehydes

A
  • Depends on the polarity of the functional group and on the chain length
  • The lower members are all water soluble
  • As the length of the non-polar hydrocarbon chain increases the solubility in water decreases
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17
Q

Why do alkanes have low reactivity?

A
  1. The C–C and C–H bonds have high bond enthalpies and are relatively strong
  2. The C–C and C–H bonds are non-polar
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18
Q

Describe, with example equations, the complete and incomplete combustion of alkanes

A
  1. Complete combustion of alkanes produces carbon dioxide and water:

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

  1. Incomplete combustion produces carbon monoxide and water:

2 C3H8(g) + 7 O2(g) → 6 CO(g) + 8 H2O(g)

  1. Incomplete combustion when oxygen is extremely limited produces carbon and water:

C3H8(g) + 2 O2(g) → 3 C(s) + 4 H2O(g)

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19
Q

What is a free radical?

A

An atom that contains an unpaired electron (no net charge) and is very reactive

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20
Q

What is a substitution reaction?

A

When another reactant takes the place of a hydrogen atom in the alkane

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21
Q

What is homolytic fission?

A

An event in which a bond breaks by splitting the shared pair of electrons between the two products producing two free radicals:

X:X → X· + X·

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22
Q

What is the reaction between chlorine and methane?

A

CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)

UV light is the required catalyst

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23
Q

What are the three steps in the reaction mechanism?

A
  1. Initiation
  2. Propagation
  3. Termination
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24
Q

What happens in the initiation process of the reaction mechanism?

A
  • Homolytic fission occurs
  • Occurs in the presence of UV light
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25
Q

What happens in the propagation process in the reaction mechanism?

A
  • Free radicals are used and produced, allowing the reaction to continue (chain reaction)
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26
Q

What happens in the termination process of the reaction mechanism?

A
  • Free radicals are removed from the mixture by reacting them together and pair up electrons
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27
Q

What are addition reactions?

A

A reaction in which a double bond is broken to add two hydrogens to a compound.

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28
Q

Describe, with an equation, the reaction of alkenes with hydrogen

A
  • Called hydrogenation
  • Alkene goes through addition reaction
  • Nickel catalyst and at 150°C

CH3CHCH2 + H2 → CH3CH2CH3

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29
Q

Describe, using an equation the reaction of alkenes with halogens

A
  • Forms dihalogeno compounds
  • Happen quickly at room temperature
  • Loss of colour of the halogen

CH3CHCH2 + Br2 → CH3CHBrCH2Br

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30
Q

Describe, using an equation, the reaction of alkenes with hydrogen halides

A
  • Form halogenoalkanes
  • React rapidly at room temperature

CH2CH2 + HCl → CH3CH2Cl

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31
Q

Describe, using an equation, the reaction of alkenes with water

A
  • Called hydration
  • Converts the alkene into an alcohol
  • Involves an intermediate
  • Heat with steam and catalyst of concentrated H2SO4

CH2CH2 → CH3CH2(HSO4) → CH3CH2OH + H2SO4

H2SO4catalyst H2O

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32
Q

How can alkanes and alkenes be distinguished by using bromine water?

A
  • Alkene mixed together with bromine water forms a clear compound, the brown colour disappears
  • Alkane mixed with bromine water stays brown coloured
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33
Q

What is the repeating unit in polymers?

A

–(–CH2–CH2–)n–

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34
Q

What are three examples of polymers?

A
  1. Polyethene
  2. Polychrloroethene
  3. Polypropene
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35
Q

How are polymers created?

A

The double bond of alkanes is broken down and many alkane molecules are put together in a long chain

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36
Q

What are the economic advantages of the reactions of alkanes?

A
  • Hydrogenation is used to manufacture margarines from oils
  • Hydration is used to form ethanol
  • Polymerisation is used to form plastics
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37
Q

Describe, using an example, the complete combustion of alcohols

A
  • Burns to produce CO2 and water

2 CH2OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(g)

38
Q

What is formed when primary alcohols are oxidised?

A

First aldehydes and if further oxidised, carboxylic acid

39
Q

What is the product of oxidation of secondary alcohols?

A

Ketone

40
Q

Are tertiary alcohols readily oxidised?

A

No.

41
Q

How is aldehyde obtained from the oxidation reaction of primary alcohols?

A

By distilling the product off as it forms

42
Q

How is carboxylic acid obtained from the oxidation of primary alcohols?

A

By heating it under reflux

43
Q

What is a nucleophile?

A

An electron-rich species that is attracted to parts of molecules that are electron deficient

44
Q

What are halogenoalkanes?

A

Saturated alkanes that contain an atom of fluorine, chlorine, bromine, or iodine bonded to the carbon skeleton

45
Q

What is meant by an electron deficient atom?

A

An atom in a polar covalent bond which loses its electrons to a more electronegative atom

46
Q

What is heterolytic fission?

A

Breaking a bond where both the shared electrons go to one of the products. Two oppositely charged ions are produced:

X:X → X+ + X:–

47
Q

What are curly arrows used for?

A

Representing the motion of an electron pair: the tail of the arrow shows there the pair comes from and the head shows where it is going

48
Q

What determines the product in a nucleophilic substitution reaction?

A

The nucleophile used to replace the halogen

49
Q

Explain the SN2 nucleophilic substitution mechanism

A
  • For primary halogenoalkanes
  • The carbon atom is relatively open to attack by the nucleophile
  • An unstable transition state is formed in which the carbon is weakly bonded to both the halogen and the nucleophile
  • The carbon-halogen bond then breaks heterolytically, releasing Cl– and forming the alcohol product

CH3Cl + OH– → CH3OH + Cl–

50
Q

What is the rate of a SN2 substitution mechanism dependent on?

A

The concentration of both the halogenoalkane and the hydroxide ion (bimolecular reaction)

51
Q

Explain the stages in SN1 nucleophilic substitution

A
  • Tertiary halogenoalkanes
  • Three alkyl groups make it difficult for the nucleophile to attack the carbon atom
  • The first step involves the halogenoalkane ionising by breaking its carbon-halogen bond heterolytically
  • The carbon atom has a temporary positive charge (carbocation)
  • The carbocation is attacked by the nucleophile, forming a new bond
  • The alkyl groups have an electron-donating (positive inductive) effect which make the carbocation stable for long enough for the new bond to form

CH3C(CH3)ClCH3 + OH– → CH3C(CH3)OHCH3 + Cl–

52
Q

Which substitution mechanism do secondary halogenoalkanes go through?

A

A mixture of both SN1 and SN2 mechanisms

53
Q

Draw a diagram of the reaction pathways between organic molecules

A

* = mechanism required

red arrow = oxidation

purple = reduction/addition of H2

green = substitution

yellow = addition

grey = elimination

blue = condensation

54
Q

Why is the hydroxide ion a better nucleophile than water?

A

Because OH– has a negative charge, H2O doesn’t

55
Q

What does the rate of nucleophilic substitution reactions depend on?

A
  1. The class of the halogenoalkane
    - Tertiary is the fastest and primary the slowest
  2. The identity of the halogen
    - Rate increases down Group 7 from the fluoroalkane to the iodoalkane
56
Q

Describe, using equations, the substitution reaction of halogenoalkane with ammonia

A
  • NH3 is a nucleophile due to the lone pair of electrons on the nitrogen atom
  • SN2
  • The substitution reaction yields in an amine:

C2H5Br + NH3 → C2H5NH2 + HBr

CH3CHBrCH3+ NH3 → CH3CH(NH2)CH3 + HBr

(CH3)3CBr + NH3 → (CH3)3CNH2 + HBr

  • Amines can further behave as nucleophiles
57
Q

Describe, using equations, the substitution reaction of halogenoalkane with potassium cyanide

A
  • CN ion is a nucleophile as it contains a lone pair and a negative charge on the carbon
  • SN2
  • The substitution yields in a nitrile compound

C2H5Br + KCN → C2H5CN + KBr

58
Q

Describe the reduction of nitriles using hydrogen and nickel

A
  • Introduction of the nitrile group is an easy way to increase the length of the carbon chain in a molecule
  • Reduction occurs using hydrogen and nickel catalyst
  • Nitrile is converted into a primary amine

C2H5CN + 2 H2 → C2H5CH2NH2

  • Nitriles are very useful intermediates (reaction pathways)
59
Q

What is an elimination reaction?

A

A reaction in which a small molecule is removed from a larger molecule, leading to the formation of an unsaturated product

60
Q

What kind of bond is often formed in an elimination reaction?

A

A carbon–carbon double bond

61
Q

Describe, using an equation, the elimination of HBr from bromoalkanes

A

CH3CH2CH2Br + NaOH → CH3CH=CH2 + NaBr + H2O

  • A hot alcoholic solvent is used
62
Q

What are the two possible mechanisms for elimination?

A

E2 (elimination bimolecular)

E1 (elimination unimolecular)

63
Q

Explain the E2 elimination mechanism for the elimination of bromine

A
  • One-step mechanism
  • Bimolecular
  • OH– ion acts as a base and accepts a proton, from the molecule
  • The carbon–bromine bond breaks heterolytically, electrons going to the bromide ion
  • The electrons from the carbon–hydrogen bond form the new bond of the double bond
64
Q

Explain the E1 elimination mechanism for bromine

A
  • Unimolecular
  • Two-step process
  • (1) Ionisation of the halogenoalkane
  • (2) Formation of the double bond
  • Rate-determining step depends on the concentration of the halogenoalkane
65
Q

What is the use of esters?

A

Food flavourings and perfumes

(also plasticisers to make plastics more flexible)

66
Q

What happens in a condensation reaction?

A

Two molecules react to form a product with the loss of a small molecule

(formation of polymers)

67
Q

What is the requirement for a condensation reaction to occur?

A

Each reactant must have a functional group that reacts with the functional group on the other molecule

68
Q

Describe the condensation reaction between carboxylic acids and alcohols

A

carboxylic acid + alcohol ⇔ ester water

CH3COOH + CH3OH ⇔ CH3COOCH3 + H2O

  • Esterification occurs
  • Formed by warming a mixture of the carboxylic acid and alcohol in the presence of concentrated sulfuric acid
  • The sulfuric acid acts as a catalyst and may also improve the yield
69
Q

What are the chemical properties of esters?

A
  • They do not have free –OH groups so they cannot form hydrogen bonds
  • They are more volatile and less soluble in water
70
Q

Describe the condensation reaction between carboxylic acids and amines

A

carboxylic acid + primary amine → secondary amide + water

CH3COOH + CH3NH2 → CH3CONH(CH3) + H2O

  • Secondary amines react to form tertiary amides
71
Q

How are polyesters formed?

A
  • When the acid has two –COOH groups and the alcohol two –OH groups
  • The chain extends in both directions forming a polyester
72
Q

How are polyamides (polypeptides) formed?

A
  • Condensation reaction of two amino acids
  • An amide link (peptide bond) is formed between the acids
  • A free –NH2 group on one end and a free –COOH gorup on the other allow the continuing the reaction by condensation to form polypeptides and ultimately proteins
73
Q

What is the economic importance of condensation reactions?

A

Esters

  • Used as food flavourings and perfumes
  • Used as plasticisers, helping to soften plastics and make them more flexible
  • Naturally occurring fats and oils are examples of esters (product of glycerol and fatty acids)
  • PET is used in synthetic fibres and the production of plastic bottles

Polyamides

  • Polypeptides form proteins
  • Synthetic polyamides include plastics such as nylon and kevlar, used in clothing, carpets, machine parts, tyre cords, ropes
74
Q

What are stereoisomers?

A

Compounds with the same structural formula but with different arrangement of atoms in space

75
Q

What kind of isomerism is present in non-cyclic alkenes?

A
  • Called geometric isomers (cis-trans isomers)
  • Restricted free rotation of the bonded groups (double bond)
  • Cis = same side
  • Trans = opposite sides
76
Q

What are geometric isomers?

A

Cis-trans isomers

77
Q

Which factors affect the physical properties of geometrical isomers?

A
  1. Polarity of the molecules
  2. The shape or symmetry of the molecules
78
Q

How does the polarity of the molecule affect the physical properties of geometrical isomers?

A
  • Affects the boiling points as it determines the strength of the intermolecular forces
79
Q

How does the symmetry of the molecule affect the physical properties of geometrical isomers?

A
  • Affects the melting point as it affects the packing in the solid state
  • Trans-isomers are able to pack more closely due to their greater symmetry → the melting point is higher
80
Q

Describe the chemical properties of geometric isomers

A
  • Generally very similar
  • Exception is butenedioic acid:
  • when cis-isomer is heated it condenses
  • when trans-isomer is heated it sublimes but no chemical change occurs
81
Q

What are other types of geometrical isomers except for linear molecules?

A

Cyclic molecules

  • Cyclopropane and cyclobutane
  • The substituted groups do not have to be on adjacent carbon atoms
  • The ring prevents rotation around the carbon atoms

Dichloro derivatives:

82
Q

What is a chiral (asymmetric) carbon?

A

A carbon that is bonded to four different atoms or groups to form a tetrahedral, or a molecule with such arrangement

83
Q

What are enantiomers?

A

The two isomers of molecules that show optical isomerism

84
Q

What is a racemic mixture?

A

A mixture that contains equal amounts of both enantiomers

85
Q

What is meant by non-superimposable molecules?

A

Molecules that have no plane of symmetry and do not line up when put on top of each other

86
Q

What are two examples of molecules that show optical isomerism?

A
  1. butan-2-ol
  2. 2-chlorobutane
87
Q

What are the properties of optical isomers?

A

Isomers have identical physical and chemical properties with two exceptions:

  1. Optical activity
  2. Reactivity with other chiral molecules
88
Q

What is meant by optical activity?

A

Optical isomers’ property of polarising light.

89
Q

How is a polarimeter used to distinguish between optical isomers?

A
  • When a beam of plane-polarised light passes through a solution of optical isomers, they rotate the plane of polarisation
    1. The sample of isomers is placed in the sample tube
    2. Plane-polarised light is passed through the sample tube
    3. Rotation of the polarisation plane occurs in the tube
    4. The light passes through a second polariser called the analyser
    5. The analyser has been rotated until the light passes through it
    6. The extent and direction of rotation brought about by the sample can be deduced from the analyser
  • Enantiomers of the same concentration rotate plane-polarised light in equal amounts but in opposite directions
  • A racemic mixture does not rotate the light because the enantiomers cancel out and the solution is said to be optically inactive
90
Q

What is a resolution? (optical isomerism)

A

A method of separating two enantiomers from a racemic mixture by reacting them with another chiral compound

91
Q

What happens when a racemic mixture is reacted with a signle enantiomer of another chiral compound?

A
  • The enantiomers produce two different products
  • Products have distinct chemical and physical properties and can be separated easily

Chemistry (13 decks)

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