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chemistry > topic 6 - organic chemistry > Flashcards

topic 6 - organic chemistry Flashcards

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1
Q

what are isomers

A

molecules with the same molecular formula but different arrangement of atoms (structural formula)

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2
Q

what are the 3 types of structural isomerism

A

chain
position
functional group

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3
Q

what is chain isomerism

A

-the carbon chain is branched in a different way
-e.g. a straight chain and a branched chain, but both have the same molecular formula
-butane and 2-methylpropane : C4H10

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4
Q

what is position isomerism

A

-the functional group is in a different position
-e.g. pent-1-ene and pent-2-ene : C5H10

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5
Q

what is functional group isomerism

A

-the position or arrangement of the atoms means that the functional group is changed completely
-e.g. alcohols and esthers

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6
Q

what are the 3 main parts to naming an organic compound

A

stem - number of carbon atoms in the longest chain containing the functional group
e.g. eth, meth, prop
prefix - showing the position and identity of any side chains
e.g. 1-methyl
suffix - an ending showing what functional group is present

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7
Q

what are the general steps to naming a molecule

A

-find the longest chain, assign a stem
-find the functional group, assign a suffix
-identify the name of any side chains
-number the principle chain so any side chain are given the lowest possible number
(side chain names appear in alphabetical order)
(if there are identical side chains, add di,tri or tetra to the prefix)
(numbers are separated from names by a hyphen)
(numbers are separated from numbers by a comma)

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8
Q

how do you name haloalkanes

A

-use the stem and suffix based on the original alkanne
-add a prefix indicating the halogens position and then the element
-bromo, chloro, iodo, fluoro
-e.g. 2-chloro-2-methylpropane

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9
Q

how do you name alcohols

A

-select the longest chain containing the OH functional group
-remove the e off the alkane name and add the suffix ol
-number the chain starting with the end nearer to the OH group
-the number is placed after the an but before the ol e.g. butan-2-ol
-add the correct prefix for any alkyl substituents e.g. 5-methylhexan-2-ol

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10
Q

define functional group

A

an atom or group of atoms that give the molecule or compound it’s distinctive and predictable properties

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11
Q

what is a homologous series

A

-a set of compounds with the same functional group
-differ by CH2
-have similar chemical and physical properties that show a gradual change
-have the same general formula

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12
Q

what is an organic compound

A

a compound that contains at least 1 carbon atom covalently bonded to at least 1 other element

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13
Q

what is a hydrocarbon

A

a molecule containing hydrogen and carbon atoms only

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14
Q

what are cycloalkanes

A

-saturated hydrocarbons
-the carbon chain forms a continuous ring

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15
Q

What is the name of the NH2 functional group

A

Amine group

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16
Q

What is a functional group

A

A group of atoms in a molecules which determines its reactivity and chemical properties

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17
Q

What are the 5 characteristics of a homologous series

A

-same functional group
-neighbouring molecules differ by CH2
-have similar chemical properties
-show a gradual change is physical properties
-same general formula

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18
Q

Why do molecules with longer carbon chains have stronger intermolecular forces

A

They have more electrons
Have stronger temporary dipoles

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19
Q

As the length of the carbon chain increases the melting point

A

Increases

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20
Q

As the length of the carbon chain increases the melting point

A

Increases

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21
Q

what are the 3 ways to convert crude oil into fuels

A

fractional distillation
cracking
refining

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22
Q

describe the process of fractional distillation

A

-crude oil is heated into a vapour
-there is a temperature gradient within the fractional column, it’s hotter at the bottom and cooler at the top
-the vapour passes up the column through a series of bubble caps
-different fractions condense at different heights depending on their boiling point

23
Q

what are the lengths and boiling points of alkanes at the top and bottom of a fractional column

A

top: shorter length chains and lower boiling points
bottom: longer length chains and higher boiling points

24
Q

why is cracking useful

A

-there is a higher demand for shorter chain alkanes than longer chain alkanes
-because they are better fuels
-so there is a surplus of long chain alkanes

25
Q

describe the process of cracking

A

-the long chain alkanesare passed through a heated catalyst (e.g. zeolite)
-for each 1 long molecule, at least 2 smaller molecules are formed alkanes and alkenes

26
Q

out of straight chain, branched and cyclic alkanes, which are the most efficient as fuels

A

-cycloalkanes are the most efficient because they burn more efficiently
-then branched
-then straight chains

27
Q

describe the process of reforming

A

-hydrocarbons are heated with a catalyst (e.g. platinum)
-straight chain alkanes are converted into branched and cycloalkanes
-the products of the reaction are usually a cyclo/branched alkane + H2

28
Q

what conditions must be present for the substitution reaction of alkanes halogenation

A

-at room temperature the mixture must be exposed to ultraviolet light
-or if the temperature is increased a reaction will eventually occur

29
Q

what is a free radical

A

a species that contains a single unpaired electron

30
Q

why is free radical substitution not an efficient reaction

A

-it is likely that further substitution reactions will occur beyond the desired product
-so the yield of the desired product will be low
-and the products will have to be separated

31
Q

what mechanism and type of reaction do alkanes undergo

A

Free radical substitution
homolytic fision

32
Q

what is the general formula for alkenes

A

CnH2n

33
Q

why type of bonds does a double bond contain

A

1 sigma bond
1 pi bond

34
Q

what is a sigma bond

A

when 2 electron orbitals from 2 different atoms overlap end on forming a covalent bond

35
Q

what is a pi bond

A

when electron orbital overlap sideways forming a covalent bond

36
Q

describe what happens to the bonds in alkenes during addition reactions

A

-the double bond becomes a single bond
-the sigma bond remains unchanged
-the pi bond electrons are used to form new bonds with another molecule
-the reaction forms a product with sigma bonds, so it is saturated
-as the product has sigma bonds and no pi bonds, it is more stable

37
Q

which are stronger, sigma bonds or pi bonds, why?

A

-sigma bonds
-because the electrons in the sigma bond is closer to the carbon atoms
-so is more strongly held by the carbon atoms

38
Q

what is the test for a carbon double bond
what is the positive and negative result

A

alkene + bromine water
positive result: the bromine water is decolourised, it goes from orange-brown to colourless
negative result: remains an unchanged orange-brown colour

39
Q

describe the test for a carbon double bond

A

-its an addition reaction between an alkene (e.g. ethene) and bromine water
-the pi bond in the double bond breaks, these electrons are now used to form a sigma bond between the carbon atom and bromine atom (twice)
-the sigma bond between the carbon atoms remain
E.g. C2H4 + Br2 = C2H4Br2

40
Q

what is hydrogenation
are there any required conditions

A

-an addition reaction where hydrogen is added to an alkene
the product is 1 alkane
-a nickel catalyst and heat are required

41
Q

describe one of the uses of hydrogenation

A

-manufacturing of margarine
-vegetable oils are unsaturated so contain a carbon to carbon double bond
-when vegetable oils undergo hydrogenation some of the double bonds become single bonds
-this changes the propterties of the vegetable oil, making it a solid

42
Q

describe halogenation reactions
are there and required conditions

A

-addition reactions between an alkene and a halogen
-the products are 1 dihalogenoalkane
-no required conditions

43
Q

describe hydration reactions
are there any required conditions

A

-addition reactions
-an alkene is heated with steam, then passed through a a catalyst of phosphoric acid (H3PO4)
-H and OH are added to the carbon atoms on the double bond
-the product is an alcohol
-the only required condition is heat

44
Q

describe addition of hydrogen halides reactions
are there any required conditions

A

-addition reaction between an alkene and a hydrogen halide
-the product is 1 halogenoalkane
-there are no required conditions

45
Q

describe oxidation to diols reactions
are there any required conditions

A

-oxidation followed by addition
-the required conditions are potassium manganate in acidic conditions (solution of dilute sulfuric acid)
-the potassium manganate provides 1 oxygen atom (oxidation)
-the acid solution provides 1 oxygen atom and 2 hydrogen atoms
-so there is an addition of 2 OH groups across the double bond
-the product is an alkanediol

46
Q

what is an electrophile

A

a species that is attracted to negative charge

47
Q

what is the mechanism of the reaction between ethene and hydrogen bromide

A

electrophilic addition

48
Q

in an electrophilic addition reaction involving alkenes when can there be more than 1 possible product formed

A

when the alkene and attacking molecule are unsymmetrical

49
Q

what does it mean when a carbocation is described as primary, secondary or tertiary

A

primary carbocation: the carbon atom with the positive charge is joined to 1 alkyl group
secondary carbocation: the carbon atom with the positive charge is joined to 2 alkyl groups
tertiary carbocation: the carbon atom with the positive charge is joined to 3 alkyl groups
tertiary carbocations are the most stable, then secondary, then primary
because alkyl groups are electron-releasing so when there are more of them the positive charge is spread more than when there is only one, when the positive charge can be spread over more atoms the carbocation is more stable

50
Q

what are the major product and minor product formed from using Markovnikoff’s rule

A

Markovnikoff’s rule: the major product will be formed through the route of the more stable carbocation (only applies to unsymmetrical alkenes and attacking molecules)
the major product is formed from the more stable carbocation
the minor product is formed from the less stable carbocation

51
Q

what are the products of homolytic fission

A

results in free radicals

52
Q

what are the products of heterolytic fission

A

results in ions

53
Q

Why do polymers have a higher melting point than their monomers

A

There are more electrons in the polymer
So stronger van der walls forces
So more energy needed to break bonds

chemistry (3 decks)

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