4.1.1 Representing the formulae of organic compounds

Question 1

Describe the molecular formula

Answer 1

The molecular formula shows the actual number of atoms of each element in a molecule.
Carbon atoms are listen first then hydrogn then the other elements in alphebetical order.

e.g. C₂H₆O

Question 2

Describe the empirical formula

Answer 2

The empirical formula gives the simplest whole number ratio of atoms in the molecular formula.
- The empirical formula can be worked out from experimental data based on contribution.
- If the Mr is available it can be used to convert thr empirical formula into the molecular formula

Question 3

Describe how to convert the empirical formula into the molecular formula

Answer 3

1. Work out the moles of each element
2. divide by the smallest (n)
3. use the ratio produced by putting it into whole numbers

If the mass of the empirical formula = the Mr
Then molecular formula is the empirical formula
If not the Mr will be a whole number multiple of the empirical formula mass

Question 4

Describe the general formula

Answer 4

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

e.g. CnH2n+2 = alkane general formula

Question 5

what is the general formula for alkanes

Answer 5

CnH2n+2

Question 6

What is the general formula for alkenes

Answer 6

CnH2n

Question 7

what is the general formula for alcohols

Answer 7

CnH(2n+1)OH

Question 8

what is the general formula for carboxylic acids

Answer 8

C nH 2n+1COOH

Question 9

What is the general formula for ketones

Answer 9

CnH2nO

Question 10

Describe the displayed formula

Answer 10

The display formula shows every atom and every bond in the structure relative to one another

Question 11

Describe the structural formula

Answer 11

A structural formula shows how the atoms are bonded to each othe, which is important for predicting reactivity.
The simplest version can be “typed”
e.g. if molecular is C₅H₁₂ then structural formula could be CH₃CH₂CHCH₃CH₃ or C(CH₃)₄

Question 12

Describe the skeletal formula

Answer 12

A skeletal formula is a simplified display formula.
all the carbon and hydrogen lables from carbon chains are removed and any bonds to hydrogen atoms are removed.
Double or triple bonds are shown by a corresponding number of lines.
In the skeletal formula:
- a line represents a single bond
- the angle between 2 bonds represents a carbon
- the end of a line represents a -CH₃ group

When a functional group is present they are shown as their symbol and a bond connecting e.g. -Cl

e.g. /\/\ = C₅H₁₂

Question 13

What is a benzene ring

Answer 13

An aromatic functional group characterized by a ring of six carbon atoms with a circle inside the skeletal formula

wrong - to do with π bonds and delocalised π-electrons

Question 14

Define structural formula

Answer 14

the minimal detail that shows the arrangement of atoms in a molecule

Question 15

define displayed formula

Answer 15

the relative positioning of atoms and the bonds between them

Question 16

define skeletal formula

Answer 16

the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups

Question 17

What is R

Answer 17

R can be used to represent alkyl groups, but also other fragments of organic compounds not involved in reactions