Topic 6 organic chemistry: Nomenclature and Alkanes

general formula of alcohols

CnH2n+1OH

what is alkenes and general formula

-unsaturated hydrocarbon : contains a double bond

-CnH2n

What are alkyl groups?

-derived from alkanes

-attached to organic molecules

-H missing

name the stem names of increasing no of carbon atoms

meth-

eth-

prop-

but-

pent-

hex-

hept-

oct-

non-

dec-

Steps to naming organic compounds:

1.Identifying the longest continuous carbon chain to determine the stem name.

2.Recognising the key functional groups to determine suffix names.

3.Numbering the carbon atoms based on the location of the functional group.(primary functional group's carbon receiving the lowest possible number.)

4.Including numbers and prefixes for any side chains present.

5.Applying multipliers like di-, tri-, and so on for multiple identical groups.

define homologous series

-Series of organic compounds with the same functional group and general formula

-each member differs by CH2 from the last

-have same chemical properties

define functional groups

atom or group of atoms which when present in different molecules causes them to have similar chemical properties

Addition

— joining two or more molecules together to form a larger molecule

Polymerisation

— joining together lots of simple molecules to form a giant molecule

Elimination

— when a small group of atoms breaks away from a larger molecule.

Substitution

— when one species is replaced by another.

Hydrolysis

— splitting a molecule into two new molecules by adding H+ and OH- derived from water.

Oxidation and Reduction

oxidation — any reaction in which a species loses electrons.

reduction — any reaction in which a species gains electrons.

what does a mechanism show?

-shows movement of electrons during a chemical reaction

-using curly arrows

Draw a reaction mechanism to show CH3Cl + NaOH ➔ CH3OH + NaCl

...

what are the different types of mechanisms

1)radical substitution : in reacting halogens in alkanes, to make halogenoalkanes

2)electrophilic addition : used in adding halogens and hydrogen halides to alkenes, to make halogenoalkanes

3)nucleophilic substitution: primary halogenoalkanes with aqueous potassium hydroxide to make alcohols and with ammonia to make amines

what are the three types of classifying agents?

nucleophiles

electrophiles

radicals

what are nucleophiles?

Electron pair donors in an organic mechanism. Attracted to electron-deficient areas

-halide ions/species that contains a lone pair of electron

-are electron rich

-react with positive ions

what are electrophiles?

Electron pair acceptor in an organic mechanism. Attracted to areas with lot of electrons/high negative charge.

-they are positive ions that react with negative ions

What is a radical?

A species with an unpaired electron. Represented in mechanisms by a single dot

-e.g. the chlorine atoms produced when UV light splits a Cl2 molecule

-because they have unpaired electrons they are very reactive

-react with positive and negative ions

how is two molecules isomers?

-same molecular formula

-but atoms are arranged differently

what are the two types of isomerism?

Structural isomerism and stereoisomerism

what are structural isomers and what are the three different types?

-same molecular formula but different structural formula

-chain isomers

-positional isomers

-functional group isomers

what are chain isomers?

-same molecular formula

-different carbon skeleton

eg: pentane and 2-methylbutane

-have similar chemical properties

-different physical properties due to change in shape

what are positional isomers?

-same molecular formula

-different position of the functional group on the carbon skeleton

-different chemical and physical properties

eg: pentan-1-ol and pentane-2-ol

what are functional group isomers?

-same molecular formula

-different functional group

-different chemical and physical properties

eg: pent-1-ene and cyclopentane

what is alkanes and general formula

-saturated hydrocarbon :contains single carbon carbon bonds

-CnH2n+2

what is bond fission?

breaking a bond

what are two ways a single covalent bond between two atoms be broken?

homolytic fission

heterolytic fission

what is heterolytic fission?

-the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair.

-the atom that receives the electron pair becomes an anion and the other becomes a cation

X-Y ➔ X+ + Y-

what is homolytic fission?

-the bond breaks evenly and each bonding atom receives one electron from the bonded pair.

-Two electrically uncharged 'radicals' are formed.

-because of the unpaired electrons the radicals are very reactive

X-Y ➔ X• + Y•

how does halogen react with alkanes to from halogenoalkanes?

-halogens react with alkanes in photochemical reactions

-Photochemical reactions are started by light — this reaction requires ultraviolet light to get going.

-A hydrogen atom is substituted (replaced) by chlorine or bromine. This is a free radical substitution reaction.

-eg: chlorine and methane react to form chloromethane

what are the three stages of the reaction mechanism?

-initiation

-propagation

-termination

what happens in initiation? draw the mechanism

1) Sunlight provides enough energy to break the Cl-Cl bond — this is photodissociation:

2) The bond splits equally and each atom gets to keep one electron — homolytic fission.

3)The atom becomes a highly reactive radical, Cl•, because of its unpaired electron.

Cl2 ➔ 2Cl•

what happens in propagation? draw the mechanism

during propagation reactions radicals are used up and created in a chain reaction

1) Cl• attacks a methane molecule

2) The new methyl radical, •CH3 , can attack another Cl2 molecule

3) The new Cl• can attack another CH4 molecule, and so on, until all the Cl2 or CH4 molecules are wiped out

Cl• + CH4 ➔ CH3• + HCl

CH3• + Cl2 ➔ CH3Cl + Cl•

what happens in termination? draw the mechanism

-collision of two free radicals does not generate further free radicals

-If two free radicals join together, they make a stable molecule

-eg: chloro/bromomethane

Cl• + CH3• ➔ CH3Cl

producing just chloromethane is difficult as further reactions occur producing a...?show the mechanisms of what happens

-mixture of products

-if there is loads of chlorine in the reaction mixture we will get di tri and tetra haloalkanes

-with free radical substitution you make dichloromethane, trichloromethane and tetrachloromethane which all have to be separated

-in addition to multiple substitutions we can also get (structural)isomers formed. this is because free radical substitution can occur anywhere on a hydrocarbon

Cl• + CH3Cl ➔ CH2Cl• + HCl

CH2Cl• + Cl2 ➔ CH2Cl2 + Cl•

how do you reduce the chances of these byproducts?

-adding excess of methane.

-This means there's a greater chance of a chlorine radical colliding only with a methane molecule and not a chloromethane molecule.

show the overall equation for this reaction

CH4 + Cl2 ➔ CH3Cl + HCl