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Chemistry > Organic Chemistry - Intro, Alkanes and Alkenes A1 > Flashcards

Organic Chemistry - Intro, Alkanes and Alkenes A1 Flashcards

Module 4

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1
Q

What is a homologous series?

A

A series of organic compounds having the same functional group but with each successive member different by CH2.

LEARN

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2
Q

What is displayed formula?

A

The actual structure of the compound showing the position of each atom and bond relative to each other.

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3
Q

What is structural formula?

A

Formula showing the arrangement of atoms minus the bonds (e.g. CH3CH(CH3)CH2CH3 ).

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4
Q

What is the skeletal formula?

A

Diagram showing just the carbon backbone

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5
Q

What is aliphatic?

A

A compound arranged in straight or branching chains (or non-aromatic rings).

NOTE: no need to learn definition, just understand.

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6
Q

What is alicyclic?

A

A compound arranged in non-aromatic rings, with or without branching chains.

NOTE: no need to learn definition, just understand.

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7
Q

What is aromatic?

A

A compound that contains a benzene ring.

NOTE: no need to learn definition, just understand.

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8
Q

What are structural isomers?

A

Compounds that have the same molecular formula but a different structural formula.

LEARN

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9
Q

What are the 3 types of structural isomers?

A

Chain isomerism
- Different chain length, caused by branching.

Positional isomerism
- Position of functional group differs along the chain.

Functional isomerism
- Position of atoms causes a different functional group. (e.g. alkenes to cycloalkanes)

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10
Q

What are alkanes?

A

A homologous series of saturated hydrocarbons that share the general formula CnH2n+2.

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11
Q

The angles in Alkanes are always ____.

Alkanes are ______ molecules so only _____ forces are present.

A

109.5 degrees
non-polar
London

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12
Q

The b.p. of Alkanes is affected by what?

A

Chain length and branching - the number of points of contact - number of intermolecular foces.

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13
Q

What is the trend in b.p. for alkanes?

A

The longer the chain, the more points of contact, so more intermolecular forces present, so higher b.p.

The more branched the molecule is, the lower the boiling point as molecules are unable to pack together as tightly as straight chains so few have fewer points of contact.

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14
Q

Alkanes have ____ reactivity because….

A

low

…sigma bonds have a high bond enthalpy and a very low polarity (C and H are close enough in electronegativity that they have non-polar bonds).

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15
Q

What is combustion?

A

An exothermic reaction caused when a fuel is oxidised by oxygen.

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16
Q

When does complete and incomplete combusion occur and what do they produce? When combusting alkanes, which releases more energy?

A

Complete occurs when there is excess oxygen, and will form carbon dioxide and water.

Incomplete occurs when there is limited oxygen and will form carbon monoxide (or Carbon) and water.

Complete combustion of an alkane releases more energy per mol than incomplete combustion.

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17
Q

What are radicals?

A

Species with an unpaired electron which makes them highly reactive.

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18
Q

What is homolytic fission?

A

HOMOLYTIC = ‘same breaking’ - each atom in a bond takes one electron from the bonded pair to form two radicals.

FISSION = splitting of a covalent bond

19
Q

What is needed to convert an alkane to a haloalkane?

A
  • UV light
  • halogen
20
Q

What is a substitution reaction?

A

When an atom/group is replaced by another atom/group.

21
Q

Describe the 3 steps of a substitution reaction involving homolytic fission.

A

1) INITIATION
- Diatomic molecules are split into halogen radicals by UV radiation.

2) PROPAGATION
- Halogen radical removes an alkane’s hydrogen forming an alkyl radical and hydrogen halide.
CH4 + .Cl –> HCl + .CH3
- Alkyl radical removes a halogen from a diatomic molecule, forming a halogen alykl and halogen radical.
.CH3 + Cl2 –> CH3Cl + .Cl
- This halogen radical reacts with many alkane molecules, causing a chain raction.

3) TERMINATION
- Two radicals react with each other to form a covalent bond and chain reaction ends.

.CH3 + .CH3 –> C2H6
.CH3 + .Cl –> CH3Cl
.Cl + .Cl –> Cl2

22
Q

What is stereoisomerism?

A

When compounds have the same structural formula but a different arrangement in space.

23
Q

Describe E/Z isomerism.

A

Occurs in alkenes (due to C=C bonding) when carbons are bonded to 2 different atoms/groups on either side.

CAHN, INGOLD AND PRELOG RULES:
E - ‘highest priority’ atoms/groups diagonally opposite.

Z - ‘highest priority’ atoms/groups on the same side.
Zee Zame Zide

Highest priority = largest atomic number/longest alkyl chain.

24
Q

What are Cis-Trans Isomers?

A

A type of E/Z isomer where there is one hydrogen on each side of the double bond.

Trans = hydrogens are diagonally opposite

Cis = Hydrogens are on the same side
(Cis has an ‘s’ sound for ‘same side’)

25
Q

What are alkenes?

A

Alkenes are a homologous series of unsaturated hydrocarbons that share the general formula CnH2n.

26
Q

What are sigma bonds?

A

When orbitals directly between bonding atoms overlap.

27
Q

What are pi bonds?

A

Sideways overlap of adjacent p-orbitals above and below the bonding carbon atoms - (weaker than sigma bonds)

28
Q

What is a double bond made out of?

A

A pi bond and a sigma bond.

29
Q

What are the properties of alkenes?

A

1) Insoluble in water
2) b.p. increases with chain length
3) Alkenes have a lower b.p. than their equivalent alkane (don’t pack as well due to shape and have less Hs so less electrons so weaker London forces)
4) More reactive than alkanes as pi-bonds are weaker than sigma bonds because the position of the pi bond makes it easier to ‘attack’ the electron pair.
5) All alkenes undergo addition reactions.

30
Q

What are the conditions and products of Hydrogenation of an alkene?

A

Condition: 150 degrees, nickel catalyst
Product: Alkanes

31
Q

Name the 4 reactions for alkenes and their reagents.

A

Hydrogenation - hydrogen
Bromination - Bromine
Hydration - Water (steam)
with Halogen Halides - HX (e.g. HBr or HCl)

32
Q

What are the conditions and products of Bromination of an alkene?

A

Conditions: Mix at RTP
Products: Dibromoalkane

33
Q

What are the conditions and products of Hydration of an alkene?

A

Conditions: High pressure and temperature, H3PO4 catalyst
Products: Alcohol

34
Q

What are the conditions and products of alkenes reacting ‘with Hydrogen Halides’?

A

Condtions: Mix at RTP
Product: Haloalkane

35
Q

What happens to bromine water when an alkene is added?

A

It is decolourised (when bromination takes place).

36
Q

What is an electrophile?

A

An electron pair acceptor (often have a delta plus).

37
Q

What is heterolytic fission?

A

The splitting of a covalent bond where one atom takes both electrons, forming a pair of ions.

38
Q

What should your curly arrows look like for homolytic and heterolytic fission?

A 
Homolytic = half head arrows 
Heterolytic = full head arrows
39
Q

Where should curly arrows be drawn from?

A

A lone pair of electrons (in the middle), a bond or a negative charge.

Note: The curly arrow should be drawn more towards the carbon the hydrogen is bonded to in alkenes.

40
Q

What happens in electrophilic addition?

A

1) An induced dipole is created in a molecule by the high density of electrons in an alkene, repelling electrons.
2) Electron pair attracted from the pi bond in the alkene to the electrophile.
3) Bond broken between the atoms unevenly in the molecule so both electrons go to the delta negative atom.
4) The negative ion uses lone pair to bond to the carbocation in the alkene.

41
Q

What are major and minor products of alkene reactions?

A

Major product = most stable as the carbocation is bonded to more carbon atoms.

Minor product = less stable as the carbocation is bonded to less carbon atoms.

42
Q

What is a primary, secondary and tertiary carbocation?

A

Primary = carbocation is bonded to one other carbon atom.

Secondary = carbocation is bonded to 2 other carbon atoms.

Tertiary = carbocation is bonded to 3 other carbon atoms.

43
Q

What is Markownikoff’s rule?

A

The hydrogen from the HX attaches to the carbon of the C=C which already has the most H atoms attached to it.

(the hydrogen attaches to where there are more hydrogens).

44
Q

When 3 steps of the radical substitution reaction occur at the same time, it results in products reacting with radicals forming what?

A
  • Longer alkane chains (e.g. C2H6)
  • Multiple substitutions of halogens on an alkane (e.g.CH2Cl2, CHCl3, CCl4)
  • Substitution in different positions (e.g. different isomers formed in reaction of chlorine and propane)

Chemistry (22 decks)

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