Laura B. Sonnichsen
Chemistry 203
NOMENCLATURE – HYDROCARBONS
1.
The number of carbons is indicated by the prefix:
C1
C2
C3
C4
C5
2.
Meth
Eth
Prop
But
Pent
C6
C7
C8
C9
C10
Hex
Hept
Oct
Non
Dec
The suffix indicates the class of compound:
ane: alkanes
ene: alkenes
yne: alkynes
3.
Alkyl groups are formally derived from the corresponding alkane by removal of one hydrogen
(CnH2n+1). [Nomenclature – replace “e” with “yl”]
CH3-CH3
CH3-CH2-CH3
4.
ethane
propane
CH3-CH2ethyl group
CH3-CH2-CH2- propyl group
Common Names: (Hydrocarbons)
Name
Structure
Alkyl Group(s)
Name
Abbreviation
Methane
CH4
CH3
Methyl
Me
Ethane
CH3CH3
CH3CH2
Ethyl
Et
Propane
CH3CH2CH3
CH3CH2CH2
n-Propyl
n-Pr
CH3 CH CH3
iso-Propyl
iso-Pr
CH3CH2CH2CH2
n-Butyl
n-Bu
CH3CH2 CH CH3
sec-Butyl
sec-Bu
CH3CHCH2
CH3
iso-Butyl
iso-Bu
tert-Butyl
tert-Bu
n-Butane
Isobutane
CH3CH2CH2CH3
CH3CHCH3
CH3
CH3 C CH3
CH3
NOTE:
n : normal
sec: secondary
tert: tertiary
iso, sec, and tert are sometimes abbreviated as i-, s-, and t-.
nomenclature(S09).docx
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February 5, 2009
Laura B. Sonnichsen
5.
Chemistry 203
IUPAC Names: (Hydrocarbons)
In the IUPAC system, a name consists of (L)-#-substituents+prefix+suffix.
Steps for naming a molecule:
A. Find the largest carbon chain. This chain is the main chain, and the prefix.
a. Example: a six carbon main chain has the prefix hex.
b. EXCEPTION: If an unstaturation (double or triple bond) is present, the chain
containing the unsaturation is ALWAYS the main chain (prefix).
c. Rings:
i. Use cyclo in front of the prefix to identify the presence of a ring.
ii. If both a ring and a straight chain are present, whichever has the most
number of carbons is the main chain (prefix).
iii. EXCEPTION: If a phenyl (benzene) ring is present with a carbon chain of
two or more that contains any other groups, the phenyl ring is the substituent.
B. Determine the suffix. This is determined by examining the class of the compound.
C. Number the main chain, giving the substituents the lowest possible numbers.
a. Chains must be numbered starting at one end. Rings should always be numbered
starting at an unsaturation or substituent.
b. If an unsaturation is present, it should have the lowest possible number.
c. If there are only alkyl substituents, then use the following method to determine the
numbering:
i. Number the chain in both directions.
ii. Locate the first substituent going in both directions.
iii. Which number is lower? This is the direction the chain should be numbered.
iv. If both are the same, continue to the second substituent and repeat. If
needed, keep going until the first numbering difference is reached.
d. If there are two ways to number the chain, then use alphabetical order to determine
the numbering.
D. Write name!
a. Write as: (L)-#-substituentprefixsuffix.
b. If more than one substituent of a particular type, use di, tri, tetra, etc. to indicate the
how many of that group. List all the position numbers in front of the substituent.
c. If more than one type of substituent, they are listed alphabetically (NOT in number
order!)
d. If more than one unsaturation of a particular type, use di, tri, tera, etc. to indicate how
many of that unsaturation. Di, tri, tetra, etc. are given between the prefix and the
suffix (leave an extra “a” before the di, etc. as a spacer). List all unsaturation position
numbers before the prefix and after any substituents. Example: 1,3-butadiene.
e. USING ALPHABETICAL ORDERING:
i. When ordering groups alphabetically, do NOT count di, tri, tetra, or other
indicators showing the number of substituents. Also, tert- and sec- are
ignored. ONLY iso and neo are counted.
f. NOTE: Separate numbers with commas; numbers and letters with hyphens.
g. The (L) part of the name is used to indicate configurational stereoisomers.
i. For alkenes, use E or Z, where appropriate. If a molecule is E or Z, you must
always include it in the name.
ii. In common names, you might see cis or trans (italicized) instead of E or Z.
Cis & trans don’t use the parantheses.
nomenclature(S09).docx
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February 5, 2009