Download As we proceed through organic chemistry we will often focus our

1
Lecture 8
As we proceed through organic chemistry we will often focus our interest on a limited portion of a
structure when the remainder of the structure is not important to the topic of discussion. Symbolic
representations for generic portions of a structure are given below and are commonly used. We will often
use these representations in this and the coming chapters.
R = any general carbon group (occasionally, it could also represent hydrogen)
Ar = any general aromatic group, (when more specificity than just R is desired)
I. Nomenclature Rules For Alkanes and Cycloalkanes
The following list provides the names for carbon chains of various lengths. They must be memorized
(through C12 for problems in this book).
a. CH4
b. CH3CH3
c. CH3CH2CH3
d. CH3CH2CH2CH3
e. CH3(CH2)3CH3
f. CH3(CH2)4CH3
g. CH3(CH2)5CH3
h. CH3(CH2)6CH3
i. CH3(CH2) 7CH3
j. CH3(CH2) 8CH3
methane (C1)
ethane (C2)
propane (C3)
butane (C4)
pentane (C5)
hexane (C6)
heptane (C7)
octane (C8)
nonane (C9)
decane (C10)
k. CH3(CH2)9CH3
l. CH3(CH2)10CH3
m. CH3(CH2)11CH3
n. CH3(CH2)12CH3
o. CH3(CH2)13CH3
p. CH3(CH2) 14CH3
q. CH3(CH2) 15CH3
r. CH3(CH2)16CH3
s. CH3(CH2)17CH3
t. CH3(CH2)18CH3
undecane (C11)
dodecane (C12)
tridecane (C13)
tetradecane (C14)
pentadecane (C15)
hexadecane (C16)
heptadecane (C17)
octadecane (C18)
nonadecane (C19)
icosane (C20)
u. CH3(CH2)19CH3
v. CH3(CH2)20CH3
w. CH3(CH2)21CH3
x. CH3(CH2)22CH3
y. CH3(CH2)23CH3
z. CH3(CH2)24CH3
aa. CH3(CH2) 25CH3
bb. CH3(CH2)26CH3
cc. CH3(CH2)27CH3
dd. CH3(CH2)28CH3
henicosane (C21)
doicosane (C22)
triicosane (C23)
tetraicosane (C24)
pentaicosane (C25)
hexaicosane (C26)
heptaicosane (C27)
octaicosane (C28)
nonaicosane (C29)
triacontane (C30)
Steps to Name an Alkane
1. Locate the longest carbon chain present. This becomes the parent name. Make sure to check at each
branch point for the longest chain path. (Unless it is obvious, count at each branch point through all
possible paths.)
Where is the longest chain? (R = substituent branch)
incorrect
2
1
R
3
R 4
12
6
8 9 10
7
11
5
This chain is longer with
12 Cs so we pick this one.
1
2
3
4
5
6
7
8
9
This chain is 10 Cs long.
10
2
Lecture 8
2. If there are several branches radiating out from a central carbon, you can count how long those
branches are and use the longest two plus the central carbon and add them all together.
4
= a central carbon position
4
5
These two branches are
equivalent in length, but
the lower one is chosen
because it has more
branches on it. It must
also be part of the longest
chain.
2
3
3
4
1
3
6
1
2
4
5
4
3
1
4
2
3
4
3
2
These two branches are equivalent
and because they are longest must
be part of the longest chain. Either
one can be used.
4 5
3
6
4
4
= part of the longest chain
longest chain = 5 + 6 + 1 = 12
parent name = dodecane
Number the longest chain from the end nearest a branch point or first point of difference. (The lowest
first number decides which end of the chain you number from.)
What end do you number from?
incorrect
2
1
R 4
12
R on C4
3
5
6
7
8
12
9 10 11
11
R on C9
10
R 9
8
7
6 5
4 3
2
1
A lower number for the substituent branch, R, is preferred. C4 is better than C9 so number from the left end.
The number will be used to specify the position of the alkyl branch.
If additional chains are present, the lowest number of the first chain determines the numbering
direction on the longest chain.
12
C3 substitution is lower than C4 substitution
11
10
R 9
8
7
6 5
4 3
2
1
The direction of the numbering is reversed because the new branch would get
a lower number, C3, at the first point of differnece, than C4 if the numbering
occurred from the opposite direction.
3. When an alkane portion is present as a substituent/branch (i.e. it is not part of the longest carbon
chain) one drops the -ane suffix of a similar length alkane and adds the suffix -yl. Alkane becomes
alkyl when it is a substituent; (ethane Æ eth + -yl Æ ethyl.) These substituent names are placed in
front of the parent name, as prefixes, with their designating numbers immediately in front of them.
Use the numbers obtained from rule 2 to show the location(s) of any substituent(s) or branch(es).
Each substituent gets a number, even if it is identical to another substituent and on the same carbon.
Hyphens are used to separate the numbers from the letters. Separate substituent position numbers
from one another with commas (if the numbers are adjacent). The substituents are listed in
3
Lecture 8
alphabetical order. The numerical prefixes (see rule 4) do not count in deciding the alphabetical order
(unless they are inside parentheses).
12
11
substituents
3-methyl
8-ethyl
8-ethyl
9-methyl
10
9
8
7
4 3
6 5
1
2
There are two one carbon branches on C3 and C9 carbons
and two two carbon branches, both on the C8 carbon. The
first branch at C3 determines the direction of numbering
because it generates the lowest possible number at the first
point of difference.
parent name = dodecane
7 C branch = heptyl
8 C branch = octyl
9 C branch = nonyl
10 C branch = decyl
11 C branch = undecyl
12 C branch = dodecyl
1 C branch = methyl
2 C branch = ethyl
3 C branch = propyl
4 C branch = butyl
5 C branch = pentyl
6 C branch = hexyl
4. For identical substituents, use the prefixes di-, tri-, tetra-, penta-, hexa-, etc. to indicate 2, 3, 4, 5, 6,
etc. of these substituents. These prefixes are not considered in deciding the alphabetical order of each
substituent (unless inside parentheses).
12
11
number of identical
substituents
2
3
4
5
6
7
etc.
10
9
8
7
6 5
4 3
1
2
8,8-diethyl-3,9-dimethyldodecane
numerical
prefix
ditritetraprntahexahepta-
5. With two or more possible longest chains of identical length, choose as the parent name the one with
the greater number of substituents. This will produce simpler substituent names.
Number from the right because
the first branch appears at C2.
7-butyl
These two branches are
equivalent in length, but
the lower one is chosen
because it has more
branches on it.
9-propyl
5-methyl
10
12 11
8
9
7
6
5
4
3
2-methyl
2
These two branches are equivalent.
Either one can be used.
1
10-methyl
8,8-diethyl
7-butyl-8,8-diethyl-2,5,10-trimethyl-9-propyldodecane
The substituent alphabetical orders are:
b > e > m > p (don't count "d" of di or
"t:" of tri-). If you do not write these in
the correct order, your structure will still
be drawn correctly from the given name.
4
Lecture 8
6.
For complex substituents (substituents that have substituents on themselves), follow the above rules
for alkanes except:
i. The -ane suffix of the subparent name is changed to -yl (see rule 3 above)
ii. The longest chain of the complex branch always uses the carbon directly attached to the parent
chain as C1. Starting at this position one would count the longest substituent chain possible, as shown
below.
iii. Parentheses are used to separate the entire complex substituent name, its numbers, its branches,
and its subparent name, from the principle parent name. A number and a hyphen precede the entire
complex substituent name in parentheses to indicate its location on the parent chain. If the complex
branch has a common name, this can be used and no parentheses are necessary, but you have to
memorize these.
iv. Prefixes do count in alphabetizing the branch names when part of a complex substituent name and
inside parentheses. This is not true for simple substituents on the parent chain.
2,10-dimethyl
5-(2-methylpropyl)
2''
3'
7-(1-ethylbutyl)
1'
10
8-(1,2-dimethylpropyl)
12 11
9-propyl
1'
parent chain = dodecane
9
1''
7
1''
3'
5
1'' = point of attachment to longest branch chain
1''
1'
6
2'
1' = point of attachment to longest chain
2'
2'
8
1'
3'
3'
1''
1'
= part of the longest chain
4'
2''
4
3
2
1
1'
Outside the parentheses the numerical prefix does not
count for alphabetical order, but inside the parentheses
the numerical prefix does count for alphabetical order.
If you do not write these prefix names in the correct order,
your structure will still be drawn correctly from the given
name.
8-(1,2-dimethylpropyl)-7-(1-ethylbutyl)-2,10-dimethyl-5-(2-methylpropyl)-9-propyldodecane
v. If identical complex substituent names are present, a different set of prefixes is used. These are
listed below. The appropriate prefix is placed before the parentheses containing the complex
substituent name.
Prefix
bistristetrakispentakishexakisetc.
Number of Identical Complex Branches
2
3
4
5
6
1' 2'
1
2
3
4
5
6
2
7
3
8
9
1
1'
10
4,4,5,7-tetrakis(1-methylethyl)decane
4
2'
6
5
1,4-bis(1,1-dimethylethyl)cyclohexane
5
Lecture 8
Examples
C C
3
C C
6 5
6
2
C
1
C
C
C C
C
1 2
C C C
C
4
5 4
C C
6 5
6
3
C
4
4
5
C
C C
3
6
3
2
C C
C
C C
6 5
C
4
5
4
C
C C
3 2 1
2
3
1
Rule 1 - The longest chain is six carbons.
Rule 2 - Number from the end closer to the
two two carbon branches, as C3 positions
instead of C4 positions.
Rule 3 - Name two carbon branches as
3-ethyl and 3-ethyl.
Rule 4 - Use the di prefix since there are two
ethyl substituents.
2
1
1
All of the above are: 3,3-diethylhexane
1
C
C 2
C
3
C C C
C C
6 5
C
6
4
5
3
In this example, the parent name would still be hexane
(six carbons long). This would be the only acceptable
parent "hexane". The chain would have to be numbered
this way because the methyl substituent gets a lower
number than any other possibility, 2-methyl. The
3,3-diethyl would come alphabetically before 2-methyl,
so would appear first in the name.
2 1
C C
C
4
3,3-diethyl-2-methylhexane
C 2
C C
1'
2' C C 3 C
C C
6 5
1
C
6
4
5
3
C C
2
1
1'
C
4
There are many ways to get this
name in this particular compound.
A slight additional modification produces two identical
parent structures. There is now a complicated branch
(a branch that has a branch) at the C3 position and
parentheses are needed.
2'
3-ethyl-2-methyl-3-(1-methylethyl)hexane
Additional Examples
1.
5
3
4
2
1
7
parent = octane
C2, C3, C5 substituents = 2,3,5-trimethyl
C4, C5 substituents = 4.5-dipropyl
alphabetical = methyl > propyl
6
8
2,3,5-trimethyl-4,5-dipropyloctane
2.
1'
11
10
9
8
2'
3
7
6 5
2
4
1'
1
2'
3'
parent = undecane
C2 substituent = 2-methyl
C4 substituent = 4-(2-methylpropyl)
C5 substituent = 5-(1,1-dimethylethyl)
C8 substituent = 8-(1-methylethyl)
1' 2'
alphabetical = C5 (dimethylethyl) > C2 methyl > C8 (methylethyl) > C4 (methylpropyl)
5-(1,1-dimethylethyl)-2-methyl- 8-(1-methylethyl)-4-(2-methylpropyl)undecane
6
Lecture 8
3.
2'
5'
4'
3'
4
5
2'
parent = dodecane
C6 substituent = 6-pentyl
C6 substituent = 6-(1,2-dimethylbutyl)
C5 substituent = 5-methyl
C4 substituent = 4-(1-methylethyl)
1'
3
2
1
1'
6
7
8
12
9 10 11
2' 1'
alphabetical = C6 (dimethylbutyl) > C5 (methyl) > C4 (methylethyl) > C6 (pentyl)
3'
4'
6-(1,2-dimethylbutyl)-5-methyl-4-(1-methylethyl)-6-pentyldodecane
Problem 1 – Provide an acceptable name for the following structures.
a.
b.
c.
d.
There are a number of specialized terms used to refer to the number of carbon structures and branches
bonded to a specific atom (carbon or nitrogen below). For nomenclature purposes we will introduce them
here, but you will also have to know some of them to predict patterns of reactivity when you start
studying organic reactions later in the course.
1. Primary patterns (1o) - If a carbon has only one other carbon attached to it, it is called a primary carbon
(1o), and if a nitrogen has only one carbon attached to it, it is called a primary amine.
R CH2 X
H 3C
CH2
1o = Primary carbons have only one carbon group attached to another carbon.
The arrows point at examples of primary carbons.
CH3
R CH3
X
H 3C
H 2C
CH2
X
H 3C
CH
CH2
X
H 3C
CH3
R NH2
CH3
NH2
C
CH2
CH3
1o = Primary amines have only one carbon group attached to a nitrogen. All of the following
nitrogen atoms are primary amines.
CH3
H 3C
H 2C
CH2
NH2
H 3C
CH
CH3
NH2
H 3C
C
CH3
NH2
X
7
Lecture 8
2. Secondary patterns (2o) - If a carbon has only two carbons attached to it, it is called a secondary carbon
(2o), and if a nitrogen has only two carbons attached to it, it is called a secondary amine.
R CH2
R CH X
R
R
H 3C
H 2C
CH2
2o = Secondary carbons have two carbon groups attached to them.
The arrows point at examples of secondary carbons.
H2C CH2
H 3C
X
CH
X
CH3CH2CH2CH2CH2 X
H 2C
CH2
H2C CH2
CH3
all Cs are 2o
2 = Secondary amines have two carbon groups attached to a nitrogen. All of the following
nitrogen atoms are secondary amines.
CH3
H
H
H
H 3C
CH N
H 3C
C N
CH3 CH2 N
o
R N H
R
H
CH3
N
CH3
CH3
CH3
CH3
CH3
CH3
3. Tertiary patterns (3o) - If a carbon has three carbons attached to it, it is called a tertiary carbon (3o), and
if a nitrogen has three carbons attached to it, it is called a tertiary amine.
R
R C
R
X
R C
R
3o = Tertiary carbons have three carbon groups attached to them.
The arrows point at examples of tertiary carbons.
H
R
CH3
H 3C
C
H 2C
CH3
X
CH3
H 3C
H 2C
C
H
CH3
CH
H 2C
both Cs are 3o
H 2C
CH3
C
X
CH3
3o = Tertiary amines have three carbon groups attached to a nitrogen. All of the following
nitrogen atoms are tertiary amines.
R
CH3
CH3
CH3
CH3
CH3
H 3C
CH N
H 3C
C N
CH3 N
CH3 CH2 N
R N R
CH3
CH3
CH3
CH3
CH3
CH3
8
Lecture 8
4. Quaternary patterns (4o) - If a carbon has four carbons attached to it, it is called a quaternary carbon
(4o), and if a nitrogen has four carbons attached to it, it is called a quaternary ammonium ion.
R
R C
4o = Quaternary carbons have four carbon groups attached to them. The arrows point at
examples of quaternary carbons.
CH3
CH2
H2C
CH3
C
CH2
H 2C
both Cs are 4o
H 3C H2C
C CH3
C
H2C
CH2
CH3
CH3
R
R
CH3
H 3C
C
CH3
CH3
4o = Quaternary ammonium ions have four carbon groups attached to a nitrogen. Such a nitrogen has
a positive formal charge. Both of the f ollowing nitrogen atoms are quaternary ammonium ions.
R
R N R
CH3
R
H 2C
CH3
CH3
N
CH2CH 2CH 2CH2CH 3
CH2
H 2C
CH2
H 2C
CH3
N
C
CH2
CH3
There are also three special names for one carbon groups having different numbers of hydrogen atoms
attached to them.
Number of attached hydrogens
CH3
= methyl, three hydrogen atoms are attached
CH2
= methylene, two hydrogen atoms are attached
C
H
methine, one hydrogen atom is attached, methine is
= "common" nomenclature, but used more frequently
and methylidene is "official" nomenclature, but used
less frequently
Frequently encountered common names for alkyl branches
1. The letter n (= normal) signifies a straight chain branch, with no subbranches on itself. If used, the “n”
is not part of the alphabetical ordering, i.e. n-propyl is alphabetized under “p”. Also the n is italicized in
typing or underlined in writing. It is generally assumed that if the n is not present, a straight chain branch
is present. Its use is disappearing and we will not use it.
CH3CH2CH2 X
n-propyl "X"
CH3CH2CH2CH2 X
n-butyl "X"
CH3CH2CH2CH2CH2 X
n-pentyl "X"
CH3CH2CH2CH2CH2CH2 X
n-hexyl "X"
9
Lecture 8
2a. The “iso“ pattern is a simple three carbon chain with only one branch or substituent on the middle
carbon. The "iso" prefix is part of the name and is used in alphabetizing the substituent name. It is not
italicized.
CH3
CH3
CH3
H C
H C
CH3
H C
X
CH2
H C
X
CH3
CH3
"iso" pattern
CH3
CH2
CH2 X
H C
CH3
CH2
CH2 CH2
X
CH3
isopentyl "X"
isobutyl "X"
isopropyl "X"
CH3
isohexyl "X"
"iso" is part of the name and used to alphabetize
Note - This pattern can be written in other shapes. These are still “iso”.
CH3
CH3
H C
X
CH3
HC
CH3 CH
X
CH3 CH
(CH3)2CH
X
X
CH3
CH3
CH3
X
b. A substituent at a secondary carbon of the four carbon straight chain is sometimes designated with
special notation. Such a substituent is prefaced with "sec", which stands for secondary. This designation
is only unambiguous for the four carbon chain. With five carbons or more it becomes ambiguous and is
not used. The “sec” portion is italicized when typed or underlined when written. Also “sec” is not used
in alphabetizing the substituent.
H3C CH CH2 CH3
H3C CH CH2 CH2
X
X
only one type of "sec"
position in sec-butyl "X"
CH3
H 3C
H2C CH CH2 CH3
3-"X"
2-"X"
sec-pentyl "X" is ambiguous
X
3. The tertiary or "tert-" or "t-" pattern has three methyl groups attached to a central carbon with a fourth
bond to a carbon or substituent group. The "tert-" or "t-" prefix is italicized (or underlined) and is not
alphabetized in a manner similar to “sec“.
CH3
CH3
C
CH3
"t-" pattern
CH3
CH3
C
CH3
X
CH3
t-butyl "X"
CH3CH2
C
CH3
X
CH3
tert-pentyl "X"
CH3CH2CH2
C
CH3
t-hexyl "X"
X
10
Lecture 8
4. “Neo” groups have three methyls and an additional fourth methylene carbon group around a central
carbon atom. The "neo-" prefix is part of the substituent name (just like iso) and is used to alphabetize
the substituent. It is not italicized. The central carbon with four other carbons attached is a quaternary
carbon.
CH3
CH3
C
CH3
CH2
CH3
C
CH3
CH2
CH3
CH3
"neo" pattern
neopentyl "X"
X
CH3
C
CH3
CH2
CH2
X
CH3
CH3
CH2
C
CH2
CH2
X
CH3
neohexyl "X"
neoheptyl "X"
"neo" is part of the name and used to alphabetize
If there is a choice, it is preferable to use systematic nomenclature and to not use the trivial names
above. However, when familiar complex substituents are present as branches on larger parent chains, the
temptation to use the simple common names is often overwhelming to avoid the complex names with
their multiple numbers, branches and parentheses. Also, other people use the trivial names and you may
need to interpret such nomenclature.
Problem 2 - Identify each of the substituent patterns below by its common name. Point out an example
of a 1o, 2o, 3o and 4o carbon and nitrogen. Also, point out an example of a methyl, methylene and methine
(methylidene) position.
a.
b.
r.
c.
d.
e.
f.
N(CH3) 2
q.
g.
(CH3)3N
p.
h.
(CH3)3C
o.
(CH3)2CH
n.
NHCH3
j.
NH2
m.
l.
k.
i.
11
Lecture 8
Naming Cycloalkanes
A ring is formed when a chain of atoms connects back on itself. This is possible with as few as three
atoms and can be of unlimited size. There are ring structures numbering in the hundreds. There are only
minor differences in the nomenclature of cycloalkanes and acylic alkanes.
1. Attach a prefix of cyclo- to the name of a cyclic alkane possessing the same number of carbons as the
straight chain name. A cyclic alkane has the carbons connected in a ring. The smallest possible ring has
3 carbons. The following are unsubstituted cycloalkanes up to C12.
=
cyclopropane
cyclobutane
cyclopentane
cyclohexane
cycloheptane
cyclooctane
=
cyclononane
cycloundecane
cyclodecane
cyclododecane
2. With only one alkyl branch, name the structure as an "alkylcycloalkane". No number is necessary
since there is only one substituent present.
t-butylcyclopentane
pentylcyclohexane
1,1-dimethylethylcyclopentane
3. With two or more alkyl substituents, number about the ring so as to obtain the lowest number possible
at the first point of difference. Alphabetic order is used to determine the number one position.
2
3
1
1-methyl-3-propylcyclohexane
6
4
5
7
8
6
9
2
5
1
4
3 2
incorrect
numbering
3
6
5
1
4
priority based on alphbetical order of branch names
5
6
4
5-butyl-2-ethyl-1-methylcyclononane
3
2
7
8
9 1
incorrect
numbering
Priority based on lowest possible number at first point of difference (5 versus 7 for butyl).
Alphbetical order is used for the branch names
4. If a chain component has more carbons than the ring, then the chain may become the parent name and
the cyclic portion a branch. However, if it is easier to name as a cycloalkane, that is acceptable.
1 2
3
4
5
6
7
8
3
4
5
3-cyclopentyloctane
2
1
1-methyl-3-(1-methylethyl)cyclopentane
or 1-isopropyl-3-methylcyclopentane
priority based on alphbetical
order of branch names
1
2
3
4
5
3-cyclohexyl-2,2,3,4,4-pentamethylpentane
12
Lecture 8
5. If the ring is classified as the substituent, the C1 carbon of the ring (for numbering purposes) is the
carbon directly attached to the parent chain. Number around the ring in the direction to give the lowest
number at the first point of difference (or the lowest number to the highest priority feature in the ring,
once functional groups are included).
2
1
4
3
5
6
7
1'
6'
8
9
parent chain numbers: 1, 2, 3, etc.
branch chain numbers: 1', 2', 3', etc.
2'
3-(4-ethyl-3-methylcyclohexyl)nonane
5'
4'
3'
6. When two substituent groups are on the same side of a cyclic structure (both on top or both on
bottom), the "cis" prefix is used. When two groups are on opposite sides (one on top, one on bottom) and
on different carbons, the "trans" prefix is used. The terms “cis” and “trans” are italicized (or underlined,
if written) and not used in alphabetizing. These terms go just before the designating number and are
separated from the number by a hyphen.
trans-1,2-dimethylcyclohexane
cis-1,2-dimethylcyclohexane
cis
trans
7. If more than two substituents are present, ambiguity will arise in the cis/trans nomenclature without a
reference point. The highest priority group is assigned an “r“ prefix in front of its position number. All
other substituents have a “c“ or “t“ specifying term in front of their position number to indicate cis or
trans relative to the reference group on the ring. All of these letters are italicized if typed or underlined if
handwritten. The letters are separated from the position numbers by a hyphen. If two similar substituents
are both on a similar position carbon and one is cis and the other is trans, the cis path is given the higher
priority and lower number (second example below). If two substituents are on the same carbon, only one
of them needs to be referenced as the other is decided by default (the first example below). We won’t use
this rule.
Cl
Br
Cl
No reference term is necessary for the
1-chloro or the 2-methyl substituents
because of the referencing of the other
substituents at those positions.
1
2
Cl
r-1-bromo-1-chloro-c-2-ethyl-2-methyl-t-3-propylcyclobutane
The cis Cl is given higher
priority than the trans Cl.
Br
3
r-1-bromo-c-2-t-3-dichlorocyclopropane
Problem 3 – Provide an acceptable name for each of the following structures. (You should be able to
name a, b, c and d). (You should know how to name a, b, c and d.)
a.
b.
c.
d.
e.
Br