Naming organic compounds (rules of the IUPAC)
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Naming organic compounds (rules of the IUPAC) Straight (continuous) chain hydrocarbons: A single path from one end C to the other end C passes through every C atom without backtracking  This is called the normal form.  The letter n- precedes the name.

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  • Naming organic compounds (rules of the IUPAC)

  • Straight (continuous) chain hydrocarbons:

  • A single path from one end C to the other end C

  • passes through every C atom without backtracking

  • This is called the normal form.

  • The letter n- precedes the name.

  • Most hydrocarbons so far have been this type.

Ex.

n-hexane

Ex.

n-hexane


  • B. Branched chain IUPAC rules:

  • The “parent name” is named after the longest

  • continuous chain of carbon atoms:

Ex.

Ex.

hexane

Parent name:

because longest

continuous carbon

chain = 3 and the

prefix is:

propane

Parent name:

because longest

continuous carbon

chain = 6 and the

prefix is:

prop-

hex-


  • The “first name” depends on:

  • a/ what is attached to the main chain;

  • b/ where it is attached; and,

  • c/ how many are attached

  • a/ What is Attached:

  • “Attachments” are called alkyl groups

  • They are alkanes with one less H atom:

  • Alkane Alkyl group

  • Name Formula Name Formula

  • methane CH4 methyl

  • ethane C2H6 ethyl

  • propane C3H8 propyl

  •  Rule: Replace –ane with –yl in name.

CH3

C2H5

C3H7


How to picture the alkyl group attachments:

Methane: methyl group:

condensed:

Ethane: ethyl group:

condensed:

Propane: propyl group:

condensed:

CH3

CH2CH3

CH2CH2CH3


Ex. Find the IUPAC name for isobutane:

C4H10

Molecular formula:

Condensed structural

formula:

CH3CHCH3CH3

parent name: longest continuous chain =

so it is:

3

propane

alkyl group:

methyl

IUPAC name:

methyl propane


b/ Where the Alkyl Group is Attached:

If there are > 3 carbon atoms, you must specify

which carbon atom the alkyl group is attached to.

This is done by numbering the carbon atoms in

the longest chain from the end that will give the

lowest number for the attached group.

Ex.

methyl group is attached

at the number 2 carbon

Use:

3

4

5

1

2

6

5

6

3

2

1

4

NOT:

IUPAC name:

2-methyl hexane


Ex.

H

H

parent name:

alkyl group:

position:

IUPAC name:

heptane

methyl

C

H

H

3

H

3-methyl heptane

H

H

H

H

H

H

H

H

H

H

H

H

H

Ex.

C

C

C

C

C

C

C

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

parent name:

alkyl group:

position:

IUPAC name:

octane

H

methyl

C

H

H

3

H

3-methyl octane


  • c/ A prefix is used to indicate the number of

  • attached groups there are of each type.

  • # of groups prefix:

  • 2 di-

  • 3 tri-

  • 4 tetra-

  • ETC

  • Ex. In: dimethyl triethylnonane,

  • di means 2 methyl groups

  • tri means 3 ethyl groups

  • nonane means a 9-C backbone

  • Then numbers are added as in the previous part

  • to specify exactly which C atom it is that each

  • of the methyl and ethyl groups are attached to.


Ex. What does 2,2,3-trimethyl pentane look like?

pentane means start with a 5-C alkane backbone

trimethyl means add 3 methyl groups

2,2,3 means place 2 methyls at the number 2 carbon

and place 1 methyl at the number 3 carbon

structural

diagram:

H

H

H

H

H

C

H

C

H

H

H

C

H

C

C

H

C

C

H

H

H

H

H

C

H

H


If more than one type of alkyl group are attached,

list them in alphabetical order in front of the parent

name. Then put in the position numbers for each.

Ex. Draw 3-ethyl-4-methylhexane

parent: hexane

alkyl groups: At position 3 put 1 ethyl

At position 4 put 1 methyl

H

H

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

C

C

H

H

H


Ex. What is the name of the compound below?

H--C-----C-----C-----C-----C-----C-----C-----C-----C--H

parent:

alkyl groups: 2 _______, both at position __

2 ________ at positions __ and __

start with parent: _______

add alkyls: _______ ______________

use prefixes: ________ _______________

IUPAC name: ______________________________

H

C

H

H

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C

C

H

H

H

C

H

H

H

H

H

C

H

H

nonane

3

ethyls

5

methyls

1

nonane

methylnonane

ethyl

dimethylnonane

diethyl

3,3-diethyl-1,5-dimethylnonane


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