Organic Chemistry Flashcards by A A

Describe what is meant by a functional group

O-H - the alcohol group
same for each molecule
all react in a similar way since they contain the alcohol group
alcohol group referred to as the functional group

The functional group is the part of a molecule which determines how it reacts

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Describe what is meant by a homologous series

Alcohols are called a homologous series

A homologous series of organic molecules have the same functional group but each successive member has an additional -CH

series of compounds containing the same functional group

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what is the hydrocarbon chain

chain of carbon atoms bonded to hydrogen atoms

length of hydrocarbon chain is different depending on the molecule

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are chloroalkanes examples of homologous series

Yes - they are
chloromethane
1-chloroethane
1-chloropropane

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describe what is meant by saturated and unsaturated hydrocarbons

hydrocarbons - family of organic molecules/compounds

hydrocarbons - covalent compounds containing only the elements carbon and hydrogen

ethane has a single covalent bond between the carbon atoms

Hydrocarbons which only have single covalent bonds between the carbon atoms are called saturated hydrocarbons

ethene has a double covalent bond between the carbon atoms

ethyne - the carbon atoms are bonded by a triple covalent bond
both of these are examples of unsaturated hydrocabons

Any hydrocarbon with a double or triple covalent bond between the carbon atoms is called an unsaturated hydrocarbon

alkanes dont have a functional group - but still counted as a homologous series

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use the rules for naming unbranched alkanes and alkenes

double bond can actually be in two different positions

to name these molecules -we have to show the position of the double bond

to do that - we have to number the carbon atoms

e.g. if double bod lies between carbon 1 and carbon 2 in a molecule

in the name use the lowest of the two numbe rs

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what are branched chain hydrocarbons

Branched chain hydrocarbons have a side-chain or branch

all bond lengths are equal

always identify the longest chain of carbon atoms
alkane with seven carbon chain - heptane
look at no. of c atoms in the side chain
one carbon atom has preficx meth -
alkyl group
state position of methyl group on main carbon chain
number the carbon atoms - number from the side/end which produces the lowest possible number

side chains listed alphabetically with lowest possible numbers

dashes between words and numbers
commas between numbers

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describe what is meant by molecular formula of organic compounds

determine these from data

The molecular formula of a compound tells us the actual number of atoms of the elements in that compound

other elements listed alphabetically

problems with the molecular formula

The molecular formula does not give us any information on the structure of the molecule (how the atoms are bonded to each other)

Different compounds can have the same molecular formula

meaning we cannot tell from the molecular formula alone which of these two compounds we are discussing/cant differentiate

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describe what is meant by empirical formula of organic compounds

The empirical formula is the simplest whole number ratio of the atoms of each element in a compound

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what is empirical formula of ethane

CH3
To determine the empirical formula - divide both these numbers by the smallest one
this gives us the ratio between the number of atoms

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a sample of hydrocarbon contained 0.48g of carbon and 0.08g of hydrogen

calculate the empirical formula

masses of element
percentage works the same way

mol = mass/mr (relative atomic mass)
divide both numbers by smallest number to determine the ratio

carbon
0.48/12.0 = 0.04 mol

hydrogen
0.08/1.0 = 0.08 mol

0.04/0.04 = 1
0.08 / 0.04 = 2

CH2 - empirical formula

masses of element
percentage works the same way

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how to use the empirical formula to determine the molecular formula

empirical formula = CH2
Relative molecular ass of compound = 28.0 gmol-1

To do this - we need the Mr of the compound - relative molecular mass

CH2 - Mr - 14 gmol-1

28/14 = 2

2 x CH2 -> C2H4 ethene

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Describe what is meant by the displayed formula of organic molecules

The displayed formula shows us the relative position of each atom plus all of the covalent bonds

the displayed formula does not show accurate bond angles

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Describe what is meant by the structural formula

rather than draw a displayed formula - scientists often use a structural formula

The structural formula shows us how the atoms are arranged but does not show us the bonds
Shows the atoms bonded to each carbon atom in turn

CH3(CH2)3CH3

CH2CLCH2CH3 - isomers
CH3CHCLCH3

CH3CH(CH3)CH3 - side chain

CH2(OH)CH2CH3
CH3CH(OH)CH3
C-OH

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Describe what is meant by the skeletal formula

The skeletal formula is the simplest possible way to represent the structure of an organic molecule

In the skeletal formula, we do not show the carbon and hydrogen atoms

Infact, the only atoms we show are in the functional group

Instead, we show the covalent bonds between the carbon atoms plus the bonds to any functional groups

dont need show every bond in functional group OH

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Describe what is meant by the general formula for a homologous series

The general formula is the simplest algebraic formula for a member of a homologous series

n - a given number

Determine the general formula for a given homologous series

Alkanes
Alkenes
Chloroalkane
Alcohols

Alkanes CnH2n+2
Alkenes CnH2n
Chloroalkane - CnH2n+1Cl

Alcohols CnH2n+1OH OR CnH2n+2O ( you need to show the functional group in the general formula - so the correct general formula for alcohols is CnH2n+1OH)

Describe what is meant by structural isomers

Structural isomers are molecules with the same molecular formula but different structural formulae

State the different structural isomers of pentane

methylbutane
dimethylpropane
pentane

state different structural isomers of pent-1-ene

Pent-1-ene
Pent-2-ene
2-methylbut-1-ene
3-methylbut-1-ene
2-methylbut-2-ene

Alkenes can also have structural isomers which are cycloalkanes

cyclopentane
methylcyclobutane

Describe different categories of structural isomers

sometimes two structural isomers can have different functional groups - ethanoic acid - methyl methanoate

Functional group isomers - molecules which have the same molecular formula but different functional groups

Chain isomers - molecules which differ in the arrangement of the hydrocarbon chain
e.g. butane and methylpropane

Position isomers are molecules which have different positions of the functional group on the hydrocarbon chain
1-chlorobutane
2-chlorobutane

Describe what is meant by stereoisomers

Stereoisomers are molecules with the same molecular and structural formula but the atoms are arranged differently in space

Types of isomers

Structural isomerism
Steroisomerism

Types of steroisomers

Geometrical isomers
Optical isomers

Describe the level of rotation in alkenes and alkanes

Alkanes Single covalent bonds are fully rotational (the covalent bond between the carbon atoms can rotate) Alkenes Unlike single covalent bonds which are fully rotational, double covalent bonds have very restricted rotation A double covalent bond can flex slightly but it cannot rotate like a single covalent bond Therefore this means that alkenes (molecules) actually exists in two different forms They are geometrical isomers of 1,2-dibromoethene E/Z naming system

Describe what is meant by E/Z isomers

E–Z isomerism is a form of stereoisomerism and occurs as a result of restricted rotation about the planar carbon– carbon double bond.

Use the CIP priority rules for naming E/Z isomers

The carbon atoms on either side of the double bond, must be attached to two different groups (if c is bonded to two H atoms e.g. LH carbon atom bonded to Br and H atom RH carbon atom bonded to a hydrogen atom and a methyl group At least one of the groups must be the same for both carbon atoms on either side of the double bond e.g. carbon atoms on either side of the double bond are both attached to a hydrogen atom Start by looking at the group which is the same on either side of the double bond If the group is on the same of the molecule - called Z isomer If the group is on the opposite side of the molecule - called E isomer E/Z system - the carbon atoms on either side of the double bond are attached to four different groups Look at the atoms attached to the carbons on either side of the double bond The element with the greatest atomic number is given the higher priority e.g. on LHS of double bond there is a chlorine and bromine atom - Cl - 35, Br - 35 So on LHS of double bond, bromine has higher priority On RHS of double bond H has Ar of 1, F has Ar of 9 So on RHS of double bond, F has higher priority Now we assign E or Z using the higher priority group In left hand isomer, the higher priority groups are on opposite sides of the molecule so this is the E isomer And in the right hand isomer, the higher priority groups are on the same side of the molecule. - so this is the Z isomer On RHS of double bond, C atom is attached to two atoms of oxygen That means we cannot establish priority based on the oxygen So we now move to the next atom If these are different, we can use these to establish priority In this case, we have a H atom and C atom C has a higher Ar than H therefore the group containing carbon has the higher priority