Chemistry (4.1): Basic concepts and hydrocarbons

Homologous series

Homologous series

have the same functional group and each successive member differs by CH₂ unit

Aliphatic hydrocarbons

the carbon atoms are joined together in either unbranched or branched chains

Alicyclic hydrocarbons

the carbon atoms are joined together in a ring structure but are not aromatic

Aromatic hydrocarbons

there’s at least one benzene ring in the structure

nomenclature

naming system for compounds

Alcohol functional group

OH

Aldehyde functional group

CHO

Alkane functional group

C-C

Alkene functional group

C=C

Carboxylic acid functional group

COOH

Haloalkane functional group

halogen

Ketone functional group

C-CO-C

Saturated

only single bonds

Unsaturated

have a C=C double bond

functional group

a group of atoms that is responsible for the characteristic chemical reactions of a compound

general formula

the simplest algebraic formula for all the organic compounds in a homologous series

Alkane general formula

C_nH_2n+2

Alkene general formula

C_nH_2n

Alcohol general formula

C_nH_2n+1OH

displayed formula

shows the relative positions of atoms and the bonds between them

structural formula

provides the minimum detail for the arrangement of atoms in a molecule

empirical formula

the smallest whole-number ratio of atoms of the elements in a compound

molecular formula

shows the numbers and types of atoms in a compound

skeletal formula

a simplified structural formula drawn by removing hydrogen atoms from alkyl chains

hydrocarbons

compounds that contain only hydrogen and carbon atoms

isomers

have the same molecular formula but different arrangement of their atoms

Types of isomers (2)

1. structural isomers

2. stereoisomers

Structural isomers

compounds with the same molecular formula but different structural formulae

What are the three kinds of structural isomer? (3)

1. alkyl groups in different places

2. functional group bonded to a different part of the chain

3. different functional group

Stereoisomers

organic compounds with the same molecular formula but have different arrangements of atoms in space

Types of stereoisomerism (2)

1. E/Z isomerism

2. cis-trans isomerism

What causes E/Z isomerism?

the restricted rotation around the double bond

Cis-trans isomerism

a type of E/Z isomerism in which the two substituent groups attached to both carbon atoms of the C=C bond are the same

Reaction mechanisms

models that show the movement of electron pairs during a reaction

curly arrows

model the movement of electron pairs during a reaction

homolytic fission

happens when each bonding atom receives one electron from the bonded pair, forming two radicals

radicals

species with one or more unpaired electrons

heterolytic fission

happens when one bonding atom receives both electrons from the bonding pair

alkanes

a homologous series of saturated hydrocarbons

What is the bond shape and angle in alkanes?

tetrahedral and 109.5

What kind of bonds are C-C and C-H bonds examples of?

sigma bonds

Are alkanes polar or non-polar and why?

non-polar because the electronegativity of C and H are similar so there are no dipoles

What forces are between alkane molecules?

London forces

In alkanes, how does increasing carbon chain length affect boiling point?

increased chain length = increased boiling point

Why does increased chain length increase boiling point?

Relative molecular mass increases and there are more surface area contacts between adjacent molecules so more energy is needed to overcome the intermolecular attraction between molecules

In alkanes, how does increased branching affect boiling point?

increased branching = decreased boiling point

Why does increasing branching decrease boiling point?

More branching means fewer surface area interactions between molecules so there are fewer induced dipole-dipole attractions

Do alkanes have high or low reactivity?

low reactivity

Why do alkanes have low reactivity? (2)

1. covalent bonds have high bond enthalpies

2. C-H sigma bonds have low polarity

Reactions with alkanes (2)

1. combustion

2. radical substitution

complete combustion

oxidising a fuel in a plentiful supply of air

incomplete combustion

oxidising a fuel in a limited supply of air

What is produced in complete combustion?

carbon dioxide and water

What is produced in incomplete combustion?

carbon (soot), carbon monoxide and water

What colour flame does incomplete combustion make due to soot?

cooler, dirty yellow flame

What colour flame does complete combustion make?

clean blue flame

Stages of radical substitution (3)

1. initiation

2. propagation

3. termination

What do alkanes react with in radical substitution?

halogens

initiation

formation of radicals

propagation

two repeated steps that build up the desired product in a side reaction

termination

two radicals collide and make a stable product

Characteristics of radical substitution

unpredictable and difficult to control

What are the reactions in free radical substitution caused by?

a very reactive radical randomly colliding with another species

conditions required for the initiation step of radical substitution

UV

alkenes

a homologous series of unsaturated hydrocarbons

How is a sigma bond formed?

between two carbon atoms using the direct overlap of the electron clouds of two atoms

How is a pi bond formed?

by the electrons in the adjacent p-orbitals overlapping above and below the carbon atoms

What do pi bonds cause alkanes to have?

restricted rotation around the double bond

Shape and bond angle of alkenes

(trigonal) planar and 120

Why are pi bonds reactive?

high electron density

What type of isomerism do alkenes show?

stereoisomerism

stereoisomerism

compounds with the same structural formula but different arrangements of atoms in space

electrophile

electron pair acceptor

Are alkanes or alkenes more reactive?

alkenes

Why are alkenes reactive?

the double bond is an area of high electron density so attracts electrophiles

Examples of electrophiles

Br₂, HBr and NO₂⁺

Are pi or sigma bonds weaker?

pi bonds are weaker

Reactions with alkenes (5)

1. hydrogenation

2. halogenation

3. hydration

4. addition of hydrogen halides

5. addition polymerisation

Hydrogenation conditions (3)

1. 150 degrees

2. nickel catalyst

3. hydrogen gas

Halogenation

an addition reaction where a halogen is added across C=C

What can halogenation be used for?

test for saturation

What is the positive test for saturation?

decolourisation

What is formed when bromine gets close to an electron-rich C=C bond?

dipole induced

hydration

addition reaction between gaseous alkene and steam

hydration conditions

high temperature and pressures and phosphoric acid catalyst

formular of phosphoric acid

H₃PO₄

Addition of hydrogen halides to alkenes

addition reaction in which a hydrogen halide is added across the C=C bond producing haloalkanes

Which carbocations are most stable?

tertiary

Which carbocations are least stable?

primary

What carbocation makes the major product?

the most stable carbocation intermediate (tertiary)

monomer

small molecules that are used to make polymers

polymers

macromolecules made from small repeating units

repeating unit

a specific arrangement of atoms that occurs in a structure over and over again

what bonds break in monomers during a polymerisation reaction?

pi bond

polymer of ethene

poly(ethene)

Uses of poly(ethene)

plastic bags and bottles

Uses of poly(propene)

ropes and crates

uses of poly(chloroethene) (PVC)

electrical cable insulation

uses of poly(phenylethane)

packaging

uses of poly(tetrafluoroethene)

non-stick coatings on cooking pans