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Chemistry A level > Module 4: Core Organic Chemistry > Flashcards

Module 4: Core Organic Chemistry Flashcards

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1
Q 
types of formula - Describe each
A) General formula
B) display formula
C) Molecular formula
D) Empirical formula
E) Skeletal formula
A

A) Formula for homologous series e.g. Cn H2n+2 for alkanes
B) Shows all atoms and bonds arranged in a space.
e.g. methane H
H C H
H
or
H
H C H
H
C)shows the quantities for atoms e.g. ethane = C2H6
D) simplest ratio of atoms in a compound e.g. Ethane = CH3
E) shows carbon atoms, bonds and hetero atoms.
e.g. propane - 1 ol don’t show Cs don’t show Hs

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2
Q

What is a hydro carbon?

A

A compound containing carbon and hydrogen only

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3
Q

What is the difference between saturated and unsaturated hydrocarbons?

A

Saturated: single bonds

Unsaturated: C=C carbon -carbon
or
multiple bonds   C (3 lines) C
etc
                               -
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4
Q

What is a homologous series?

A

A family of compounds with similar chem. properties whose successive memories differ by the addition of a -CH2 - group.
e.g. Alkanes - the simmplest homologous seies.

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5
Q

Waht is a functional group?

A

part of the organic molecule that’s largely responsible for the molecule’s chem. properties.
e.g. H H H H H H H
H C C C H H C C C N
H OH H H H H
alcohol - OH
functional group
amine - NH2 functional group

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6
Q

What are he 3 types hydrocarbons can be classified as?

A

aliphatic - carbon atoms are joined to each other in unbranched (straight/branched chains
alicyclic - carbon atoms are joined to each other n ring (cyclic) structures.
aromatic - some or all of the carbon atoms are found in a benzene ring.

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7
Q

What are the 3 homologous series of aliphatic hydrocarbons hat you should be aware of?

A

Alkanes - containing single c-c bonds
Alkenes -containing at least one c=c bond
Alkynes - containing at least one c three lines c bond

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8
Q

What do stems, prefixes, and suffxies show when naming hydrocarbons/organic compound?

A

The stem of the name indicates the no. carbon atoms in the longest continuous chain in the molecule.
A prefix can be added before the stem, often to indicate the presence of side chains/a functional groups.
A suffix is added after the stem to indicate functional groups

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9
Q

How do you name compounds containing functional groups?

A
  1. identify longest unbranched chain of carbon atoms. The stem is now the name of the corresponding alkane
  2. Identify any functional groups and any alkyl side chains, and select the appropriate prefixes/suffixes for them.
  3. No. any alkyl groups and functional groups to indicate their position on the longest unbranched chains.
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10
Q

name some common functional groups

A

Alkene C=C -ene
Alkyl side chain (alkane) (-CH3 methyl)
Aryl group containing benzene - phenyl
Alicyclic group with saturated cycloalkane cyclo - (e.g.CY-Cyclohexyl)
Haloalkane - Cl-Br-I chlor-bromo-iodo-
Carbonyls: c=o
carboxylic acid = O
- C - OH - COOH -oic acid
ketone c-c-c -C(CO)C- -one
aldehyde =O
- C - H -CHO -anal
amine - NH2 -NHR - NR2 amino - - amine
nitrile - CN -nitrile
acyl chloride =O
- C - CL -COCL -oxyl chloride
ester =O
- C - O - C -COOC -oate
Alcohols CnH2n + 1 e.g. propan -1-ol OH
prop-1an-1-ol OH
an-ol

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11
Q

What are structural isomers.?

A

Compounds with the same molecular formaulae but different structural formulae.
May same/different functional groups

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12
Q

How can covalent bonds be broken?

A

Homolytic fission
or
Heterolytic fission
Bonds broken but new bonds are formed in the products.

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13
Q

What is homolytic fission?

cleavage

A

Each of the bonded atoms takes one of the shared pair of electrons from the bond.
* each atom now has a single unpaired electron
* an atom or groups of atoms with an unpaired electron is called a radical
e.g. fission of C-C in ethane
H3C - CH3 leads to H3C* + * CH3
radicals

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14
Q

What is heterolytic? (cleavage)

A

when a covalent bond breaks by heterolytic fission, one of the bonded atoms takes both of the electrons from the bond.
* The atom that takes both electrons becomes a negative ion
* The atom that doesn’t take the electrons becomes a positive ion
e.g. fission of C-Cl bond in chloromethane (CH3Cl)
H3C-Cl leads to H3C+ + Cl-
ions

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15
Q

What is the reaction mechanism?

A

How the reaction takes place

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16
Q

What is a free radical?

A

An atom /species with an unpaired electron - they’re very reactive

17
Q

What are alkanes?

A 
main components of natural gas and crude oil
One of most stable organic compounds
Very unreactive
Mainly used as fuels
general formula CnH2n + 2
18
Q

Properties of alkanes:

What is the bonding in alkanes?

A
  • single covalent bond-type of covalent bond called a sigma bond
    sigma bond is the result of an overlap of 2 orbitals, each overlapping orbital contains 1 electron.
    Each C atom in a bond has 4 sigma bonds either C-C or C-H
19
Q

What is the shape of alkanes?

A

3D tetrahedral shape around each carbon atom (109.5)

  • The shapes aren’t rigid - can rotate around each sigma bond.
  • zig-zag shaped often (or V shaped)
20
Q

What are the variations in boiling points of alkanes?

A
  • b.p. increase as chain length increases
  • use fractional distilation
  • …. butane
21
Q

Elimination:

A

involves the removal of a small molecule from a larger one.
one reactant molecule forms 2 products
(see card for formulae)

22
Q

What effect does branching have on b.p.?

A
  • branched isomers have lower b.p.
  • fewer surface points of contact between molecules of the branched alkanes - therefore fewer London forces
  • branches get in the way and prevent them getting close together, decline intermolecular forces
    (diagram on card)
    more branching, less SA of contact, and therefore weaker London forces
23
Q

Substitution:

A

An atoom/groups of atoms is replaced by a differrent atom/group of atoms
see card for example

24
Q

3 types of reaction:

Addition

A

2 reactant join together to form one product

see card for example formaula

25
Q

What are curly arrows?

A

Used to show movement of electrons

see card for pictures

26
Q

What are the cahn ingold prelog (CIP) valus for naming organic compounds ? (E/z isomerism)

A
  • Look about the C=C
    • heaviest substituents have the highest priority
    • hydrogen always has lowest priority
    • with alkyl chains, the longest carbon chain has highest priority
      -E - stereoissomerism
  • highest priority atoms on opposing sides
  • Z - stereoisommerism
    • highest priority atoms on the same sidess
      see card for diagram
27
Q

What is Cis/Trans isomerism in alkenes?

A

Alkyl groups on the same side of the double bonds are cis-alkenes
Alkyl groups on the opposing side are trans-alkenes
see card for diagram

28
Q

Saturated and unsaturated hydrocarbons skeletal formulae:

A

IN saturated hydrocarbons, groups can rotate about a single bond.
when there are double bonds (unsaturated), free rotation cannot occur
see card for diagram

29
Q

Why are alkanes so unreactive ?

A

Don’t react with most common reagents:

  • C-C and C-H delta minus bonds are strong
  • C-C bond are non-polar
  • the electronegativity of carbon hydrogen is so similar that the C-H bond can be considered to be non-polar
30
Q

Describe the complete combustion of alkanes:

A

Need O2 ad heat to initiate

  • need plentiful supply of O2
  • gives out het and co2 + H2O
  • CO2 contributes to global warming/greenhouse effect
    e. g. C7H16 (l) + II02 (g) - 7CO2 (g) + 8H2O (l)
31
Q

Describe the incomplete combustion of alkanes

A
  • Need limited O2 and Heat
  • produces CO + H2O or C + H2O
  • CO= toxic gas/poisonous/colourless/odourless
  • C = soot/produces low level smog/reduces sunlight to earth/global warming
  • e.g.
    C7H16 (l) + 7 1/2 O2 (g) - 7CO(g) + 8 H2O (l)
    C7H16 (lO + 42(g) - 7C (s) + 8H2O (l)
32
Q

How do alkanes react with halogens?

A

IN the presence of sunlight. UV radiation present in sunlight provides the initial energy for a reaction to take place.
e.g. CH4 (g) + Br2 (l) - CH3Br(g) + HBr (g)
methane bromomethane
This is a substitution reaction, as a hydrogen atom in th alkene has been substituted by a halogen atom

33
Q

Bromination of methane is an e.g. of radical substitution.
3 stages:
Describe each stage
Step 1: Innitiation

A
  • Covalent bond in bromine molecule broken by homolystic fission
    each bromine takes one electron from the pair - 2 reactive bromine radicals
    Br-Br - (UV) BR     + BR *
  • shows the electron n the radical

Cl2 - (UV) 2Cl

34
Q

Bromination of methane is an e.g. of radical substitution.
3 stages:
Describe each stage
Step 2 Propogation

A

1) CH4 + Br* - *CH3 + HBr
2) CH3 + Br2 - CH3Br +Br
1) A bromine radical reacts with a C-H bondiomethane, forming a methyl radical, *CH3, and Cl molecule. hydrogen bromide, HBr.
2) each methyl radical reacts with another bromine molecule forming the organic product bromomethane and a new bromine radical.

New bromine radical then reacts with another CH4 molecule as in the first step 1) and the 2) steps continue to cycle through in Cl chain reaction. Termintion whenever 2 radicals collide.
Roughly 1 million propogation cycles before termination.

1) CH4 + Cl* - *CH3 + HCl
2) Cl2 + CH3 - CH3Cl _ Cl

35
Q

Bromination of methane is an e.g. of radical substitution.
3 stages:
Describe each stage
Stage 3: Termination

A
  • 2 radicals collide, forming molecule with all electrons paired. No of possible termination steps with diff. radicals in the reaction mixture.
  • Br* + Br - Br2
    CH3 *CH3 - C2H6
    *CH3 +    Br - CH3Br
    This process stops the reaction
    Cl     + CH3 - CH3Cl
    2Cl     - Cl2
    2CH3* - C2H6
36
Q

Limitations of radical substitution in organic synthesis;
Describe both
Further substitution:

A

In the mechanism for bromomethane, CH3Br, was formed in the 2nd propogation stage.
Another bromine radical can collide with a bromomethane molecule, substiuting a further hydrogen atom to form dibromoethane, CH2Br2.
further substitution can continue until all hydrogen atoms have been substituted. Result is a mixture of
C3Br, CH2Br2, CHBr3 and CBr4

37
Q

Substitution at different positions in a carbon chain

A

For methane, all 4 hydrogen atoms are bonded to the same carbon atom, so the only one monobromo compound, CH3Br, is possible. With ethane, only monosubstituted produt, C3H5Br is possible.
If the c chain is longer we will get a mixture on monosubstituted isomers by substitution at diff. position in the c chain. e.g. pentane could form 3 monosubstituted isomers. e.g. isomers of bromopentane
With further substitution they’re even more possibilities which can form 2 diff. dibromo isomers.

Chemistry A level (6 decks)

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