AS chemistry unit one point four

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define empirical formula

the simplest whole number ratio in which atoms in a compound combine together
define molecular formula

a formula that tells us the number of atoms of each different element that make up a molecule of a compound
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
Define displayed formula

the formula of a compound drawn out so that each atom and each bond is shown
define homologous series

a set of organic compounds with the same functional group . the compounds differ in the length of their hydrocarbon chains
define functional group

an atom or group of atoms in an organic molecule which is responsible for characteristic reactions for that molecule
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
organic chemistry is the

study of compounds containing carbon combined with other elements
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
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
functional groups
functional group - name
alkane - a
alkene - b
haloalkane - c
- a) -ane
- b) -ene
- c) bromo- , chloro- , iodo-
number of C atoms - name
1
2
3
4
5
6
- meth
- eth
- prop
- but
- pent
- hex
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) CH₂CH₂CH₃
- g) propyl
- ... butyl , pentyl , hexyl
number of identical side chains

2
3
4
- di
- tri
- tetra
name - methane
homologous series -
molecular formula -
structural formula -
empirica formula -
displayed formula
- alkane
- CH₄
- CH₄
- CH₄
name - ethane
homologous series -
molecular formula -
structural formula -
empirical formula -
displayed formula -
- alkane
- C₂H₆
- CH₃CH₃
- CH₃
propane
homologous series -
molecular formula -
structural formula -
empirical formula -
displayed formula -
- alkanes
- C₃H₈
- CH₃CH₂CH₃
- C₃H₈
name the first 6 alkanes
- methane
- ethane
- propane
- butane
- pentane
- hexane
the alkanes are

hydrocarbons - this means they only contain carbon and hydrogen atoms
what type of bond do alkanes have between the carbon atoms

single covalent
alkanes have the general formula

C_nH_2n+2
the alkanes all have names ending in

ane
for straight chain alkanes the beginning of the name tells you

the number of carbon atoms in the chain
if the chain is branched it's said to have a

side chain
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 .
for example methylbutane has

a main chain of four carbon atoms and a side chain of one carbon atom
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
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
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
give the displayed and structural formula for 2-methlybutane
- CH₃CH(CH₃)CH₂CH₃
give the structural , molecular and displayed formula for 2,3-dimethylpentane
- CH₃CH(CH₃)CH(CH₃)CH₂CH₃
- C₇H₁₆
the alkenes are also

hydrocarbons like the alkanes
alkenes have a .......... between two of the carbon atoms

a double covalent bond
alkenes have the general formula
- C_nH_2n
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
what is the structural , displayed , molecular formula and empirical of ethene
- CH₂=CH₂
- C₂H₄
- CH₂
write down the molecular formula , displayed formula , structural formula and empirical formula of 3-methylbut-ene
- CH2=CH(CH3)CH3
- C₅H₁₀
but-2-end displayed formula
but-1-end displayed formula
the functional group for alkenes is

C=C
the haloalkanes are

compounds containing carbon , hydrogen and a halogen atom
haloalkanes have the general formula

C_nH_2n+1X where X is a halogen atom
displayed formula for chloromethane
displayed formula 2-bromobutane
displayed formula 1 chloropropane and 2 chloropropane
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
isomerism occurs

when two or more organic molecules have the same molecular formula but different arrangements of atoms
the type of isomerism that we deal with in unit 1 is

structural isomerism
structural isomerism occurs when

two or more organic molecules have the same molecular formula but different structural formula
there are 3 types of structural isomerism
- chain isomerism
- position isomerism
- functional group isomerism
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
for example there are two chain isomers of C₄H_{10 ,}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
for C₅H₁₂there are 3 possible chain isomers
- the carbon atoms can be arranged in a straight chain forming pentane , as a chain of four atoms with a side chain forming methyl butane or as a chain of 3 atoms with 2 side chains forming dimethylpropoane
chain isomers are isomers where the

chain remains the same but the position changes
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}
positional isomerism occurs when

a functional group can be in more than one position on the carbon chain
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
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
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)
but-2-ene also shows a different type of isomerism called

stereoisomerism only in chem 2 and chem 4

Author

ghoran

254382

Card Set

AS chemistry unit one point four

Description

revision

Updated

2013-12-30T13:09:59Z

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