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define empirical formula
the simplest whole number ratio in which atoms in a compound combine together
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define molecular formula
a formula that tells us the number of atoms of each different element that make up a molecule of a compound
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define structural formula
a way of writing the formula of an organic compound in which bonds are not shown but each carbon atom is written separately with the atoms or groups of atoms attached to it e.g. butane-2-ol is written CH3CH2CH(OH)CH3
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Define displayed formula
the formula of a compound drawn out so that each atom and each bond is shown
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define homologous series
a set of organic compounds with the same functional group . the compounds differ in the length of their hydrocarbon chains
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define functional group
an atom or group of atoms in an organic molecule which is responsible for characteristic reactions for that molecule
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what is an isomer
one of two or more compounds with the same molecular formula but different structural formula i.e. the same atoms are arranged differently in space
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organic chemistry is the
study of compounds containing carbon combined with other elements
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carbon is an unusual element which has the ability to
form chain and ring structures by joining carbon atoms together . this ability means that a very large number of organic compounds exist
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for unit one you need to be familiar with three different homologous series
- alkanes
- alkenes
- haloalkanes
- however it's useful to know about
- alcohols , aldehydes , ketones , carboxylic acids , (primary) amines and nitriles too
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functional groups
functional group - name
alkane - a
alkene - b
haloalkane - c
- a) -ane
- b) -ene
- c) bromo- , chloro- , iodo-
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number of C atoms - name
1
2
3
4
5
6
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side chains
number of C atoms - structure - name
1 - b - c
2 - d - e
3 - f - g
- b) -CH3
- c) - methyl
- d) CH2CH3
- e) ethyl
- f) CH2CH2CH3g) propyl
- ... butyl , pentyl , hexyl
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number of identical side chains
2
3
4
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name - methane
homologous series -
molecular formula -
structural formula -
empirica formula -
displayed formula
- alkane
- CH4CH4
- CH4
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name - ethane
homologous series -
molecular formula -
structural formula -
empirical formula -
displayed formula -
- alkane
- C2H6CH3CH3CH3
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propane
homologous series -
molecular formula -
structural formula -
empirical formula -
displayed formula -
- alkanes
- C3H8 CH3CH2CH3
- C3H8
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name the first 6 alkanes
- methane
- ethane
- propane
- butane
- pentane
- hexane
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the alkanes are
hydrocarbons - this means they only contain carbon and hydrogen atoms
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what type of bond do alkanes have between the carbon atoms
single covalent
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alkanes have the general formula
CnH2n+2
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the alkanes all have names ending in
ane
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for straight chain alkanes the beginning of the name tells you
the number of carbon atoms in the chain
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if the chain is branched it's said to have a
side chain
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the side chain is named
methyl , ethyl etc depending on the number of carbon atoms it contains . this is then put in front of the main chain .
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for example methylbutane has
a main chain of four carbon atoms and a side chain of one carbon atom
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if there is more than one position that the side chain could attach to the min chain then
it is given a number . this is counted from the end of the chain in order to make the number of the side chain as small as possible . remember the chain is the same backwards so for example if there are 3 main carbon atoms and the side chain was attached to the 3rd carbon atom the number would be 1
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if more than one side group of the same kind is attached to the chain then
the prefix di- , tri- etc. is used in front of the name of the side chain
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here is the structure of an organic compound name it and write down the molecular formula and structural formula
what is the other displayed formula
- 3-ethyl-2-methylpentane
- CH3CH2CH(C2H5)CH(CH3)CH3
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give the displayed and structural formula for 2-methlybutane
- CH3CH(CH3)CH2CH3
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give the structural , molecular and displayed formula for 2,3-dimethylpentane
- CH3CH(CH3)CH(CH3)CH2CH3 C7H16
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the alkenes are also
hydrocarbons like the alkanes
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alkenes have a .......... between two of the carbon atoms
a double covalent bond
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alkenes have the general formula
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the alkenes are named in the same way as the alkanes except that
their name ends in -ene . The position of the C=C double bond is numbered if there is more than one place where it can go in a molecule . The numbering is such that it has the smallest number possible
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what is the structural , displayed , molecular formula and empirical of ethene
- CH2=CH2
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write down the molecular formula , displayed formula , structural formula and empirical formula of 3-methylbut-ene
- CH2=CH(CH3)CH3
- C5H10
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but-2-end displayed formula
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but-1-end displayed formula
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the functional group for alkenes is
C=C
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the haloalkanes are
compounds containing carbon , hydrogen and a halogen atom
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haloalkanes have the general formula
CnH2n+1X where X is a halogen atom
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displayed formula for chloromethane
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displayed formula 2-bromobutane
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displayed formula 1 chloropropane and 2 chloropropane
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if the halogen has more than one of the same halogen atom then
the halogen is numbered di- , tri- , tetra- etc as with the side chains in alkanes
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isomerism occurs
when two or more organic molecules have the same molecular formula but different arrangements of atoms
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the type of isomerism that we deal with in unit 1 is
structural isomerism
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structural isomerism occurs when
two or more organic molecules have the same molecular formula but different structural formula
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there are 3 types of structural isomerism
- chain isomerism
- position isomerism
- functional group isomerism
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chain isomerism occurs when
two or more molecules have the same molecular formula but different arrangements of the carbon chain . typically this will involve straight chain and branched chain structures
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for example there are two chain isomers of C4H10 , as the carbon atoms can be arranged in a straight chain forming ....... or as ....................
- butane or as a chain of three carbon atoms with one side chain forming 2-methyl propane
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chain isomers are isomers where the
chain remains the same but the position changes
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C4H8Cl2 has 6 possible position isomers
- CH3CH2CH2Cl2 CH3Cl2CH2CH3
- CH2ClHClCH2CH3
- CH2ClCH2CH2CH2Cl
- CH2ClCH2CHClCH3
- CH3CHClCHClCH3
- we have had 1-1 dichlorobutane , 2-2 dichlorobutane , 1-2 dichlorobutane , 1-4 dichlorbutane , 1-3 dichlorobutane and 2-3 dichlorobutane . there are also possible chain isomers which haven't been drawn
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positional isomerism occurs when
a functional group can be in more than one position on the carbon chain
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you must consider positional isomerism when
the molecule contains a chain of four or more carbon atoms or when the functional group is a halogen which can be in different positions on the chain
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there are 3 possible functional group isomers of C3H6O
- CH3COCH3 which is propanone which is a ketone
- CH3CH2CHO which is propanal which is an aldehyde
- CH2=CHCH2OH which is pro pen-3-ol which is an alkene/alcohol
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C4H8 has 2 position isomers , 1 functional group isomer and 1 chain isomer
but-1-ene (position isomer) but-2-ene (position isomer)
cyclobutane (functional group isomer)
- methylpropene (chain isomer)
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but-2-ene also shows a different type of isomerism called
stereoisomerism only in chem 2 and chem 4
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