Orgo 1 Study Guide

Topics: Acetic acid, Alcohol, Ether Pages: 95 (5574 words) Published: November 19, 2013
Introduction to Alkane Nomenclature
A. Determining the Priority of Functional
Groups.

What's in a name?
3-ethyl-5-(1-methylpropyl)-4,4-dimethylnonane

Too big a subject to cover on one sheet! This
paper will focus on alkanes. Determining
functional group priority will be the subject of
a subsequent sheet.

suffix

http://masterorganicchemistry.com

D. Applying the Lowest Locator Rule

F. Dealing With Branched Substituents
(the IUPAC Way)

Number the chain from one end so as to provide
the lowest locator possible for the first substituent.

Treat each branched substituent as its own
naming problem.
Carbon #1 of the branched substituent will be
where it meets the main chain.

2

1

3

4

5

6

6
7

7

5

2

4

1

3

B. Applying the Chain Length Rule
the NUMBERS are called "locators"
items in BLUE are called "substituents".
the name in RED at the end is called the suffix.

9

7

8

6

5

3-methyl heptane

4
3

This also applies for subsequent substituents,
if either direction would give the same number.

2
1

The purpose of this sheet is to demonstrate the rules by which alkanes are named.

4-ethyl-6-methylnonane
ORDER OF BUSINESS
A. Determine the priority of functional groups (not covered here since we're dealing with alkanes only)
B. Find the longest linear chain of your molecule, or the largest ring (whichever is greatest). This is the Chain length rule which defines both the "main chain" and also the suffix.
-tiebreaker: where more than one "path" along the molecule leads to the longest chain, the main chain is the one that contains the most substituents. C. Identify the substituents along your main chain. Substituents are classified according to length of carbon chain and the suffix "yl" is attached. D. Number your chain from one of the ends. The LOWEST LOCATOR RULE determines which end is chosen as carbon #1: "Number the chain such as to provide the lowest possible locators for the chain."

-tiebreaker for lowest-locator rule: alphabetization
E. Multiple instances of substituents are given the prefixes di, tri, tetra, etc. -note: must have locator for all substituents. Example: 1,1-dimethyl is correct. 1dimethyl is incorrect. F. Branched substituents are numbered and named seperately from the main chain, and put in brackets.

G. The FINAL name is assembled such as to arrange the substituents in alphabetical order.
-"di", "tri", "tetra" are ignored for alphabetization purposes. -prefixes like "n", "tert", "i" and "sec" are ignored for alphabetization purposes. THE EXCEPTION is "isopropyl" and "isobutyl". For some reason these count as "i" - not covered here, but this is also where one puts in descriptors like "cis", "trans", (R), (S) (E), (Z) and so on.

Names for Hydrocarbon Chains and Rings
1

methane

2
4
6

heptane

8

octane

9

nonane

10
11

butane

Where more than one "longest chain" exists,
the more substituted chain is chosen as
the "longest chain"

isopropyl

4

5

R

sec-butyl

( )n

1

6

7

5

4

3

isobutyl

R

2

3

4

5

6

6
7

7

5

2

4

1

3

3-ethyl-5-methylheptane NOT 3-methyl-5-ethylheptane
1

2

1

NOT
1-ethyl-2-methylcyclobutane
1-methyl-2-ethylcyclobutane

Multiples of the same substituent are given the
prefixes "di", "tri", "tetra", etc. The lowest locator
rule still applies.
2

1

tert-butyl

propyl
6
5

4 3

2

1

R

tert-pentyl

9

8

In certain instances, you may see the trivial names isopropyl, isobutyl, tert-butyl, tert-pentyl used.
e.g. 4-isopropyl-3-methyl-5-tert-pentylnonane.
The official IUPAC nomenclature system will never let
you down. It would probably be best to just go with that.

3

4

5

6
7

1

2

3

4

6
5

*** there seems to be some degree of confusion
on this point. Both "1-butylcyclopropane" and
"1-cyclopropylbutane" are commonly used. If...
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