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IUPAC nomenclature. Dr Margaret A.L. Blackie [email protected] Naming of the Alkanes. This step is not necessary for the alkanes – there is no functional group. . Naming of the alkanes. 1. Identify the main functional group. 2. Identify the longest unbroken carbon chain. 7 – carbon chain.

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iupac nomenclature

IUPAC nomenclature

Dr Margaret A.L. Blackie

[email protected]

slide3
This step is not necessary for the alkanes – there is no functional group.

Naming of the alkanes

1. Identify the main functional group

2. Identify the longest unbroken carbon chain

7 – carbon chain

8 – carbon chain

octane

base

slide4
NB: If the first substituent (side chain) has the same number, use the second substituent to separate the two etc …

3. Number the chain so that the first substituent has the lowest possible number

1

8

7

2

3

6

4

5

4

5

6

3

7

2

8

1

First substituent at carbon no. 2

First substituent at position no. 3

Correct numbering:

Substituents at 2, 5 and 6

slide5
4. Identify the substituents (side chains and the position on the main chain or ring)

1

2

3

4

5

6

7

8

2-methyl

5-ethyl

6-methyl

slide6
5. Use the prefixes (di-, tri-, tetra-) depending on the number of identical substituents bonded to the main chain

1

2

3

4

5

6

7

8

2-methyl

5-ethyl

6-methyl

2,6-dimethyl

5-ethyl

slide7
6. Write down the side chains in alphabetical order, preceded by the number: (don’t write down di-, tri-, tetra-etc. in alphabetical order)

1

2

3

4

5

6

7

8

5-ethyl-2,6-dimethyloctane

Dimethyl comes after ethyl, becausee is before m – thed of di is not considered.

slide8
The name should not be separated (there are some exceptions which will be addressed later.)

Numbers separated by a comma

Dimethyloctane is written as one word

5-ethyl-2,6-dimethyloctane

Numbers separated from words by a hyphen (N shows a position and is considered as a number when naming the amines and amides)

Note: The name is WRONG if any one of these three rules are disobeyed!

slide9
Important: The name is WRONG if any one of these rules are disobeyed!

5-ethyl-2,6-dimethyloctane

What is wrong with the names below?

5-ethyl-2-6-dimethyloctane

5,ethyl,2,6,dimethyloctane

Name is wrong – the hyphen between the numbers are incorrect

The name is wrong – the comma between a number and a word is incorrect

5-ethyl-2,6-dimethyl octane

Name is wrong – There should be no space between dimethyl and octane

slide11
The longest unbroken carbon chain is not necessarily straight

Longest straight chain contains only 5 carbons

Longest unbroken chain contains 8 carbons

Therefore the name is octane and not pentane

slide12
If there are two options for an unbroken carbon chain:

Choose the chain with the most side chains as the base

Two substituents

Three substituents

Correct name: 2,6-dimethyl-4-propyloctane

Incorrect: 3-methyl-5-isobutyloctane

slide13
If there is no difference in the number of the position of the first side chain, look at the following side chain, if there is no difference at the second, look at the third, etc.

2

5

1

6

5

2

4

3

3

4

6

1

Correct numbering

First substituent is at position 2 in both numberings

Second substituent at positions 3 and 4 respectively.

Correct name : 2,3,5-trimethylhexane

slide14
When there is no difference in the numbers of the positions of the substituents : choose the numbers according to alphabetical order of the substituents, that is the first substituent alphabetically gets the lowest number

5

2

1

1

6

5

2

3

4

4

3

6

3-methyl-4-ethylhexane

3-ethyl-4-methylhexane

Correct name

slide16
At grade 12 level the following step is unnecessary, but is included for educators.

Identifying the main functional group is the first step in naming the compound.

Functional groups are prioritised according a list (see next slide)

The main functional group is the functional group with the highest priority.

The base is the longest unbroken carbon chain containing the main functional group.

slide17
FUNCTIONAL GROUPS

Highest to lowest priority

slide18
The highest priority group must get the lowest possible number

Subsituents:

3-bromo

4-methyl

1

2

3

4

5

Base – pentan-2-one

Number from left to right

Main functional group – ketone – suffix ‘one’

Longest unbroken carbon chain containing the main functional group – 5 carbons - ‘pentane’

Correct name:

3-bromo-4-methylpentan-2-one

slide19
1

2

3

4

5

correct name:

3-bromo-4-methylpentan-2-one

3-bromo-4-methyl-2-pentanone is also acceptable

It is better to write the number directly in front of the main functional group

slide20
1

2

3

4

5

Correct name:

3-bromo-4-methylpentan-2-one

Consider:

Main functional group – ketone – prefix ‘one’

Longest unbroken carbon chain containing the main functional group – 5 carbons – unsaturated chain - ‘pentene’-

Base – pent-4-ene-2-one

correct name:

3-bromo-4-methylpent-4-ene-2-one

slide21
Number or no number?

Number necessary because the carbonyl group can be at position 2 or 3

Main functional group: ketone – prefix ‘one’

correct name: Pentan-2-one

Pentan-1-al is NOT acceptable

No number on the aldehyde because the carbonyl group must be on the first carbon

Main functional group : aldehyde – prefix ‘al’

correct name: Pentanal

Revise: the main functional group always gets the lowest possible number. The carbonyl group is always at the end or beginning of the chain, therefore it must be in position number 1.

slide22
Number or no number?

But-1-ene is a possibility, so the number is important.‘

correct name: But-2-ene

There is no alternative, propene is prop-1-ene

The locant is redundant in this particular case and should be dropped.

The redundancy is associated with this particular molecule not the nature of the functional group so inclusion of the locant is acceptable

correct name: Propene

slide23
H

H

H

C

C

C

H

H

2

C

C

C

H

C

C

H

3

H

H

H

H

Questions

  • On the previous slide But-2-ene and But-1-ene are called… ?
  • Give a brief explanation for the names given in question 1.
  • Write down the molecular formula for the above compounds.
  • Write down the structural formulae for 2 more possible structures.
  • Name the structures completed in question 4.

Answers

  • ISOMERS
  • Isomers are compounds with the same molecular formula but different structural formulas .
  • 4. Write down the structural formulae for 2 more possible structures.

2-MethylPropene

Cyclobutane

slide24
Carboxylic acids and derivatives

Carboxylic acids

Propanoic acid

Propanoate ion

Propanoyl chloride (not for exam)

slide25
Identify carboxylic acid that produces the ester

This part is named as with the corresponding ion - propanoate

Methylpropanoate

Identify the substituent on the carboxylate oxygen

This part is named as the alkyl group – methyl

Esters

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