Chemistry - 3.3.1: Introduction to Organic Chemistry

Why is carbon so special?

Has 4 electrons on its outer shell, so forms 4 covalent bonds + carbon-carbon bonds are relatively strong and non-polar

Displayed formula

A formula that shows the relative positions of each atom in a molecule (number of lines represents the type of bond)

Structural formula

Shows the unique arrangement of atoms in a molecule in a simplified form, without showing all the bonds - each carbon is written separately with atoms/groups attached to it (e.g. CH3CH3 - ethane)

Skeletal formula

Straight lines used to represent carbon-carbon bonds - carbon atoms assumed to be where bonds meet. Hydrogen and carbon-hydrogen bonds are not drawn

Why use a skeletal formula rather than displayed structural formula?

For more complex molecules, displayed structural formulae can become time-consuming to draw; these are faster and easier

What do curly arrows represent?

The movement of a pair of electrons - starts from a lone pair of electrons/covalent bond, then moves towards a positively charged area of a molecules to form a new bond (draw from lone pair of electrons to middle of bond or vice versa)

What is the lone pair of electrons in an organic molecule attracted to?

The positive end of a polar bond, written as Cδ+

Free radicals

Fragments that form when a covalent bond breaks in such a way that one electron goes to each atom that forms the bond - they have an unpaired electron and are usually extremely reactive

2 features of reaction mechanisms

1. Free-radicals (unpaired electrons in radicals)
2. Curly arrows

3 steps to name an organic compound

1. Identify the root - the longest unbranched hydrocarbon chain/ring (if it is a ring, add the prefix cyclo-)
2. Identify any side groups - add them as a prefix and number them based on locant. Order prefixes in alphabetical order
3. Identify the functional group of the compound - add its suffix

Functional group

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

7 functional groups and their suffixes

1. Alkanes (C2H2n+2): -ane (ethane)
2. Alkenes (C=C): -ene (ethene)
3. Halogenoalkanes (have halogen as a prefix, no suffix): -ane (chloroethane)
4. Alcohol (-OH): -ol (ethanol)
5. Aldehyde (-CHO): -al (ethanal)
6. Ketone (-CO): -one (ethanone)
7. Carboxylic acid (-COOH): -oic acid (ethanoic acid)

How do you draw the functional group of an aldehyde?

C=O and C-H

How do you draw the functional group of a ketone?

C=O

How do you draw the functional group of an alcohol?

O-H

How do you draw the functional group of a carboxylic acid?

C=O, C-O-H

What does the symbol R mean?

A hydrocarbon chain of any length

Locant

A number used to represent the position of any branching in a chain and the position of any functional group.

Where does the locant go for a side group?

As a number before the side group prefix e.g. 1-methyl

Where does the locant go for a functional group?

After the prefix but before the suffix e.g. propan-1-one

Homologous series

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

In a homologous series, what does each member differ by?

CH2

What is the effect of the length of the carbon chain on each member of a homologous series?

- It has little effect on the chemical reactivity of the functional group
- It affects physical properties

What is the effect of chain length on melting and boiling point?

As the number of carbon atoms increases, melting point and boiling point increases as more electrons means stronger intermolecular forces

What is the effect of chain branching on melting and boiling point?

It reduces melting and boiling point as the molecules pack together less well

Isomers

One of two or more compounds with the same molecular formula but different arrangement of atoms in space

2 types of isomerism

- Structural isomerism: having the same molecular formula (same number of atoms) BUT different structure (e.g. different locants for side groups)
- Stereoisomerism: having the same structural formula but different arrangement of the atoms and bonds in space

What are the 3 sub-divisions of structural isomerism?

1. Positional isomerism: the same functional groups are attached to the same carbon chain at different positions (different locants)
2. Functional group isomerism: different functional groups (but same number of atoms)
3. Chain isomerism: a different arrangement of the hydrocarbon chain (different branches)

What are the 2 types of stereoisomerism?

1. E-Z isomerism: Z means the substituents of a C=C are on the same side (symmetrical, together), E means the substituents are on opposite sides (reflected, opposite)
2. Optical isomerism

Why are Z- and E- isomers separate compounds?

Substituent groups cannot rotate around a double bond (restricted rotation around C=C bond) so Z- and E- isomers are not easily converted from one to the other.

Why are there only E-Z isomers if there is a carbon-carbon double bond?

Substituent groups joined by a single bond can rotate around the single bond.

Hydrocarbon

A molecule or compound which consists of hydrogen and carbon only

General formula for alkanes

CnH2n+2

General formula for alkenes

CnH2n

General formula for cycloalkanes

CnH2n

Cahn-Ingold-Prelog priority rules

The atom/group on each side of the double bond with the higher Ar or Mr is given higher priority - used to determine if a compound is an E or Z isomer

Give 5 features of a homologous series

1. Same general formula
2. Chemically similar / similar chemical reactions
3. Same functional group
4. Molecules increase by CH2
5. Trend in physical properties

Give the order of priority when naming organic compounds in descending order.

1. Carboxylic acids
2. Aldehydes
3. Ketones
4. Alcohols
5. Alkenes

How do you name a dione?

Alkane-x,y-dione (e.g. hexane-2,5-dione)

How do you name a diol?

Alkane-x,y-diol

How do you name a diene?

Alka-x,y-diene