Download NOMENCLATURE VI This exercise covers the basics of organic

NOMENCLATURE VI
This exercise covers the basics of organic nomenclature. It is primarily based upon the IUPAC system
(the names under IUPAC rules are called systematic names). In a few cases there are special names,
these special names are the common names and, in general, were in use before the IUPAC system was
developed. Steps I through VII are basic to all organic nomenclature and you should pay particular
attention to these steps. Each new type of organic molecule simply adds one or two extra steps to
these seven. Once you have mastered the first basic steps, the rest is much easier.
BASICS
I. Chains
In most cases, the root of the name comes from the longest continuous chain (“straight chain”) of
carbon atoms in the compound. A straight chain is one that can be traced from one end of the
compound to the other with backtracking. Any carbon atoms not a part of this chain are parts of
branches. The naming of the straight chain is based upon the number of carbon atoms. This root also
serves for branches.
No. of C's
1
2
3
4
5
Root
meth (form)
eth (acet)
prop
but
pent
No. of C's
6
7
8
9
10
Root
hex
hept
oct
non
dec
Additional information must be added to the appropriate root to complete the name of the compound.
The roots “form” and “acet” are used in special cases that will be discussed later. In general, these
two roots are not true IUPAC.
II. Suffixes
Adding a suffix to the root indicates the type of compound. Each type of compound has its own
unique suffix. For most hydrocarbons (compounds containing only carbon and hydrogen) the basic
suffixes are:
-ane Æ alkane (Hydrocarbons with only single bonds)
-ene Æ alkene (Hydrocarbons with a carbon-carbon double bond)
-yne Æ alkyne (Hydrocarbons with a carbon-carbon triple bond)
Double bonds and triple bonds are examples of functional groups. The importance of functional
groups presented later.
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IIa. Cyclo Compounds
Cyclo compounds have a prefix. If the “straight chain” is in the form or a non-aromatic ring, combine
the prefix cyclo with the root. For now, a non-aromatic ring will be considered any ring of carbon
atoms that does not have alternating single and double bonds.
Example Cyclobutane
H2C
CH2
H2C
CH2
Cyclo compounds may occur as cis and trans isomers similar to those in the alkenes covered below.
III. Branches
If not all the carbon atoms are in a continuous chain, the compound is a branched compound. If there
is more than one chain (branched) then look for:
a. The longest chain that contains a functional group (see later)
b. The longest chain (greatest number of carbon atoms not in branches).
Example The following will appear in the next three examples.
C
C
C
C
C
C
C
C
C
C
C
C
C
Longest chain is in boldface 9 C's Æ nonane
If there are two chains of the same length, pick the one with the most substituents (branches).
If there are no branches present sometimes, an n- may be in front of the name of the hydrocarbon
portion of the molecule (common name).
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IV. Numbers
Number the longest chain from one end to the other with the following considerations:
a. The lowest number goes to any functional group.
b. The lowest number(s) go to the branch(es)
Example For the above example the numbering of the chain (boldface carbon atoms)
would be:
1 2 3 4 5
6
7 8 9
Do not alter assigned numbers later.
V. Name Branches
The root for the name of a branch is determined in I above; simply count the number of carbon atoms.
The name is finished by adding a -yl suffix to the root.
Example In the above example, there are three branches.
2 methyl groups
1 ethyl group
a. Arrange the branches alphabetically.
b. If there is more than one of a particular type use a prefix also (di-, tri-, tetra-,
This does not alter the arrangement from part a.
c. Indicate the position of each branch with a number from step IV. Each
get its own number even if it is identical to one already used.
Example In the above example this gives:
etc.).
branch must
5-ethyl-2,2-dimethylnonane
a. ethyl before methyl
b. 2 methyl groups = dimethyl
c. three branches = three numbers
Separate numbers from other numbers by commas and numbers are separated from letters by a dash.
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VI. Special Names for Branches
Certain branches have special names. Some of these are:
CH3 CH
CH3
CH3 CH
isopropyl
secondary butyl (or sec-butyl)
CH3
CH2 CH
CH2 CH3
CH3
CH3
CH3 C
isobutyl
CH3
tertiary butyl
(or tert-butyl)
Note: Be careful on these, it is possible to draw these in many different ways.
VII. Halides
Similar rules apply to the alkyl halides (compounds of C, H, and one or more halogens-F, Cl, Br, or I).
The halogens are treated exactly the same as branches. Indicate the different halogens as:
F
Cl
fluoro
chloro
Br
I
bromo
iodo
Nonsystematic names for alkyl halides assume that the hydrocarbon portion of the molecule is a
branch upon a halide ion.
Example
CH3 CH
CH3
Cl
This could be:
2-chloropropane (systematic)
or
isopropyl chloride (nonsystematic)
The preceding steps outline the basic procedures of organic nomenclature covered in this class. The
following material extends this basic procedure to compounds containing various additional functional
groups. In general, each of these functional groups will be more important than the preceding
functional groups. (This will not always be true, but for now assume that it is true.) In nomenclature,
numbering of a chain must give the most important functional group the lowest possible number.
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Alkenes
Alkenes are hydrocarbons containing at least one carbon-carbon double bond. The longest chain must
contain the C=C (unless a more important functional group is present). The name will end in an -ene.
Use a number to indicate the position of the double bond (lowest possible), with the position of the
double bond being indicated by the lowest numbered carbon atom of the double bond. Once
numbered do not renumber.
Example (Hydrogens left out for simplicity-not an acceptable final answer on an exam.)
C
C
C
C
1-butene
C
C
(double bond between numbers 1 and 2)
C
2-butene
C
(double bond between numbers 2 and 3)
NOTE:
C
C
C
1-butene
C
(Not 3-butene)
No numbers are necessary for the double bond in a simple cycloalkene as the double bond is always
between carbon atoms 1 and 2. (Numbers would be needed for all double bonds if more than one is
present.) Be careful not to mistake an aromatic substance for a cycloalkene.
If there is more than one C=C use a prefix on the -ene
C
C
C
C
C
C
C
C
1,4-octadiene (Note each double bond gets its own number)
Alkenes may form geometric isomers. There are two general types of geometric isomers: cis and
trans. Cis means on the same side, and trans means on the opposite side. (Cycloalkanes may also
have cis and trans isomers.)
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1-butene–no cis or trans isomers. (H’s always cis and trans)
H
H
C
H
C
H
H
C
C
H
H
H
2-butene
H
H
C
H
C
C
H
C
H
H
H
H
cis-2-butene
(The methyl groups (or hydrogen atoms)
are on the same side of the double bond.)
H
H
C
C
H
C
H
H
H
C
H
H
trans-2-butene
(The methyl groups (or hydrogen atoms)
are across the double bond from each
other.)
Make sure that only groups directly attached to the doubled bonded carbon atoms are use to determine
if a molecule is cis or trans. In addition, if a molecule is not drawn to indicate whether it is cis or
trans, it is not necessary to specify which it is.
One alkene has a special (common) name: CH2=CH2 (ethylene). There are special names such as this
one to learn in addition to the systematic names (ethene in this case).
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Alkynes
Alkynes are hydrocarbons containing a carbon-carbon triple bond. Alkynes follow the same rules as
alkenes except that the ending is -yne. There are no cis/trans isomers for alkynes.
Example 1-chloro-2-butyne
CH3 C
C
CH2 Cl
There is one special name: acetylene (C2H2).
Aromatics
Aromatic compounds contain one or more aromatic rings. For this class an aromatic ring will be
indicated by a ring of six carbon atoms connected by alternating single and double bonds (resonating)
or a six membered ring with a circle in it. Aromatic compounds are not limited to six membered rings,
but only such materials will be a part of this discussion.
In most of the cases examined here, the IUPAC names are the same as the common names.
The simplest aromatic presented here is benzene (C6H6). Benzene has six carbons in a ring each
carbon has a single hydrogen. Other compounds form by replacing one or more of the hydrogens. If,
for example, replacing one of the hydrogens with chlorine the compound becomes chlorobenzene (the
carbon to which the chlorine is attached is automatically number one so no number is needed in the
name). Thus naming benzene derivatives is similar to the nomenclature discussed above.
If two or more of the hydrogens is replaced each of the replacements needs to have its position
indicated by a number (even though one of the numbers must be a one). Thus replacing two of the
hydrogens of benzene with bromines gives the formula C6H4Br2. There are three isomers with this
formula; they are:
1,2-dibromobenzene
1,3-dibromobenzene
1,4-dibromobenzene
You should draw each of these and prove to yourself that there are no others. Do not to forget to
number around the ring to give the smallest numbers.
In many cases, it is possible to use common names for the disubstituted aromatics. The common
names use words (or letters) in place of the numbers. The above three dibromobenzenes have the
following common names:
ortho-dibromobenzene
meta-dibromobenzene
para-dibromobenzene
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o-dibromobenzene
m-dibromobenzene
p-dibromobenzene
Either the name or the single letter abbreviation may be substituted for 1.2-, 1,3- or 1,4-.
Note: Even when the single letter abbreviation is used, pronounce the entire name when naming the
compound.
The benzene ring may be a branch. In this case, remove one of the hydrogens and attach the ring to
something else. A benzene ring present as a branch is a phenyl group (C6H5-).
The only other aromatic hydrocarbon covered here is toluene. Toluene forms by replacing a hydrogen
from benzene with a methyl group (C6H5CH3). The carbon with this methyl group is automatically
number one (this number one is not in the name).
Nomenclature for toluene derivatives is similar to benzene derivatives. Thus, when a hydrogen from
one of the ring carbons (not from the methyl) is replaced by, for example, a bromine the following
isomers could be formed (C6H4BrCH3):
ortho-bromotoluene
meta-bromotoluene
para-bromotoluene
2-bromotoluene
3-bromotoluene
4-bromotoluene
Changes on the methyl carbon of the toluene give a benz root. For example, branching on the methyl
carbon (C6H5CH2-) gives a benzyl branch.
Derivatives
Derivatives are organic compounds containing other elements in addition to carbon, hydrogen and
halogens. These other elements are part of functional groups. Functional groups are normally the
place where a molecule will react. The functional group normally gets the lowest number when
numbering the chain, and it must be part of the longest chain (this is true even when another chain
contains more carbon atoms). Only functional groups containing oxygen and/or nitrogen will be
considered at this time.
For indicating the formulas of various derivatives, it is common practice to use an R to indicate a
hydrogen or hydrocarbon part of the molecule. In some cases more than one R may be needed; if this
is the case they may be designated R and R’ etc.
Oxygen Derivatives
Alcohols
Alcohols or organic compounds where one of the hydrogens has been replaced by a hydroxyl group.
The general formula for an alcohol is R-O-H
There are two ways to name alcohols. The IUPAC system requires the final -e be removed from the
name of the hydrocarbon and an -ol be put in its place. For the common name, the hydrocarbon
portion is named as a branch on an alcohol.
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Example
H
1-propanol
or
H
H
H
C
C
C
H
H
H
n-propyl alcohol
O
H
Multiple numbers and prefixes (di, tri, etc.) are necessary if more groups are present.
Example
H
1,3-propandiol
O
H
H
H
C
C
C
H
H
H
O
H
The presence of other groups may complicate the numbering.
Example
3-iodo-2-propen-1-ol
I
H
C
C
C
H
H
H
O
H
1 = position of alcohol group, there is no room for it in front of the prop.
(The alcohol is the most important group present, so it gets the lowest
number.)
2 = double bond between C2 and C3. This must be before the prop.
3 = position of I
Replacing one hydrogen on an aromatic ring with an OH gives a phenol. The simplest phenol is the
compound phenol (C6H5OH). The carbon to which the hydroxyl group is attached in number 1.
Phenols may look like alcohols, but they often behave differently.
If an -OH replaces one of the hydrogens on the methyl group of toluene the compound is benzyl
alcohol.
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Ethers
Ethers are organic compounds where one oxygen is placed between two carbon atoms. This gives the
general formula: R-O-R'. When naming an ether both R and R’ are named as branches (-yl) suffix and
separated placed before the word ether.
Example
CH3CH2-O-CH3
ethyl methyl ether
Example
CH3CH2-O-CH2CH3 diethyl ether
Example
C6H5-O-CH2CH3
(alphabetical)
ethyl phenyl ether
Carbonyl Derivatives
These are oxygen-containing organics containing a carbonyl group.
C
O
Carbonyl group
Aldehydes
Aldehydes have the general formula:
R
C
O
H
R may also be an H.
The carbonyl carbon must be number 1 so no number is needed.
Aldehydes are named similar to alcohols except that an -al suffix is used in place of an -ol suffix.
Example
(The carbonyl C must be number 1.)
propanal
H
H
H
C
C
C
H
H
H
O
Common names use the suffix -aldehyde instead of -al (also, form- and acet- are the preferred roots).
Example
C6H5CH2CHO
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phenylethanal or
phenylacetaldehyde
Three special names are important here:
HCHO
formaldehyde
methanal
CH3CHO
acetaldehyde
ethanal
C6H5CHO
benzaldehyde
benzaldehyde (This is one of the cases
where the systematic name is the
common name.)
Ketones
Ketones have the general formula:
R
C
O
R'
Thus, a minimum of three carbons are needed.
Again, as in aldehydes, the carbonyl carbon receives the lowest number. Naming is the same as for
alcohols except that an -one suffix is used.
There is one special name that you will need to know:
CH3COCH3
propanone
acetone
(Note the acet- root even though
three, not two, carbons are involved.)
Carboxylic Acids
The general formula for a carboxylic acid is:
H
O
C
O
R
(R may also be an H)
The carbonyl C is automatically number 1.
Carboxylic acids are named like alcohols except that the suffix is -oic acid.
Special names and IUPAC names for the two simplest carboxylic acids are:
HCOOH
formic acid
methanoic acid
CH3COOH
acetic acid
ethanoic acid
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Two other important carboxylic acids are benzoic acid (C6H5COOH) and oxalic acid (HOOCCOOH =
H2C2O4).
The loss of the acidic hydrogen from an acid produces a carboxylate ion. The carboxylate ion is
named by replacing the -ic acid with -ate.
Example
HCOOCH3COO-
formate ion
methanoate ion
acetate ion
ethanoate ion
Esters
The general formula for an ester is:
R
O
C
O
R'
(R’ may be a hydrogen, but not R)
The naming of an ester relates to how an ester forms. Esters form by the reaction of an acid and an
alcohol. In the general formula, R, is from the alcohol (named as a branch), and, R', is from the acid
(named as a carboxylate ion).
Example
O
H
CH3 C
+
O
O
O
CH3
H
CH3 C
CH3
O
H
+ O
H
acetic
acid
methyl
alcohol
methyl
acetate
ethanoic
acid
methanol
methyl
ethanoate
This is condensation reaction. In a condensation reaction, splitting out a small molecule and joining
two groups.
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Nitrogen Derivatives
There are two major types of nitrogen derivatives: amines and amides. Amines are similar to alcohols
or ethers except that N replaces O. Amides are similar to esters except that N replaces the
noncarbonyl O.
Amines
Amines are ammonia derivatives just as alcohols are water derivatives. In these compounds replace
one or more of the hydrogens by an organic group.
IUPAC nomenclature uses an -amine suffix, common nomenclature names all of the organic groups as
branches. In the IUPAC system, label additional groups on the nitrogen with an N. Do not forget,
only the carbon atoms get numbers.
Example
CH3CH2-NH2
ethylamine
ethanamine
CH3CH2-NH-CH3
ethylmethylamine
(alphabetical)
N-methylethanamine
If a -NH2 group is attached to a larger molecule, and it is not to be named as an amine, this group is
called an amino group.
A benzene ring with one of the hydrogens replaced by an amino group (C6H5NH2) is aniline. If one of
the carbons, and its attached hydrogen, from benzene is replaced by a nitrogen (C5H5N) pyridine
forms. Pyridine is still aromatic and the nitrogen occupies position number 1.
Amides
The general formula for and amide is:
R
C
R'
O
N
R"
(Any, or all, of the R’s may be hydrogen)
Amides form in a method analogous to esters (even though the exact reaction will not work directly).
Amide nomenclature is therefore similar to ester nomenclature. Naming amides is done by dropping
the -oic acid (or -ic acid) from the name of the corresponding acid and replacing it with -amide.
Indicate substituents on the nitrogen with an N.
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Example
CH3 C
N
CH3
O
H
N-methylacetamide
H
C
N
O
CH3
or
CH3
N,N-dimethylformamide
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N-methylethanamide
or
N,N-dimethylmethanamide
PRACTICE SET VI-1
Draw the structure of each of the following:
1. 2-methylhexane
2. 2,3,4-trimethylpentane
3. 1-ethyl-3-methylcyclohexane
4. 1-chloro-2-butene
5. 1,5-dibromocyclohexene
6. 5-methyl-1-hexyne
7. isopropyl alcohol
8. 4-phenyl-2-pentanol
9. 3-bromophenol
10. tert-butyl phenyl ether
11. propanal
12. 2-methylbenzaldehyde
13. 2-pentanone
14. 4-hexenoic acid
15. potassium acetate
16. ethyl acetate
17. Dimethyl ethyl amine
18. methyl propanate
19. Benzene
20. Toluene
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(For additional practice do both the
condensed and structural formulas)
PRACTICE SET VI-2
Draw the structure of each of the following:
1. isopropyl bromide
2. 2,3,5-trimethyl-4-propylheptane
3. 2-methylcyclohexanol
4. 3-chloro-1-octene
5. 4,4-dimethyl-1-pentyne
6. 3-phenyl-2-propen-1-ol
7. diethyl ether
8. 3,5-dimethylcyclohexene
9. butanone
10. 2-methylpropanal
11. 4-methylhexanoic acid
12. methyl p-chlorobenzoate
13. methanamine
14. N,N-dimethylacetamide
15. 3-chloropropyne
16. 2-hexene
17. trans-2-pentene
18. 3-methyl-2-heptene
19. 2-chloro-3-methylpentane
20. 3-ethyl-3-methylhexane
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(For additional practice do both the
condensed and structural formulas)
PRACTICE SET VI-3
Name each of the following:
1. CH3-CH2-CH2-CH2-CH2-OH
2. CH3-CH2-CHO
3.
CH3
CH3 CH2 CH
CH2 CH
CH2 CH2 CH2 CH3
CH2 CH3
4. CH3-CH2-CH2-COOH
5. CH3-CH2-CH2-C6H5
6. CH3-C6H5
7. CH3-CH2-CH=CH-CH3
8. C6H5OH
9. CH3-CH2-CH2-COO-CH3
10. CH3-CH2-CH2-CH2-CH2-O-CH2-CH3
11. CH3-CHBr-CHCl-CH2-CH3
12. CH3-CO-CH3
13. CH3-CH2-CH2-CH2-CH2-CO-NH-CH2-CH3
14. CH3-CH2-CH2-CH2-NH-CH3
15. CH3-O-CH(CH3)2
16. CH3-CH2-CH3
17. CH3-CH2-CH2-CH2-CH(CH3-CH2)-CH2-CH2-CH2-CHO
18. CH3-CH2-CH2-CH2-CH2-COO19. ClC6H4NH2
(3 names)
20. CH3-CH=CH-CH2-CH2-OH
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PRACTICE SET VI-4
Draw and name each of the isomers of the following:
1. C5H12
2. C5H10
3. C5H8
4. C3H4Cl2
5. C4H10O
6. C4H11N
7. C5H10O
(do only those containing a carbonyl group)
8. C4H8O2
(do only the acids and esters)
9. C4H9NO
(do only the amides)
10. C5H9O2Na
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