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Home , Cyclodecane, Cyclononane, Cycloundecane, Icosane

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 and 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 (C1) k. CH3(CH2)9CH3 (C11) u. CH3(CH2)19CH3 henicosane (C21) b. CH3CH3 (C2) l. CH3(CH2)10CH3 (C12) v. CH3(CH2)20CH3 doicosane (C22) c. CH3CH2CH3 (C3) m. CH3(CH2)11CH3 (C13) w. CH3(CH2)21CH3 triicosane (C23) d. CH3CH2CH2CH3 (C4) n. CH3(CH2)12CH3 (C14) x. CH3(CH2)22CH3 tetraicosane (C24) e. CH3(CH2)3CH3 (C5) o. CH3(CH2)13CH3 (C15) y. CH3(CH2)23CH3 pentaicosane (C25) f. CH3(CH2)4CH3 (C6) p. CH3(CH2)14CH3 (C16) z. CH3(CH2)24CH3 hexaicosane (C26) g. CH3(CH2)5CH3 (C7) q. CH3(CH2)15CH3 (C17) aa. CH3(CH2)25CH3 heptaicosane (C27) h. CH3(CH2)6CH3 (C8) r. CH3(CH2)16CH3 (C18) bb. CH3(CH2)26CH3 octaicosane (C28) i. CH3(CH2)7CH3 (C9) s. CH3(CH2)17CH3 (C19) cc. CH3(CH2)27CH3 nonaicosane (C29) j. CH3(CH2)8CH3 (C10) t. CH3(CH2)18CH3 icosane (C20) dd. CH3(CH2)28CH3 triacontane (C30) Steps to Name an

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)

2 incorrect 1 3 R

2 4 6 8 10 R 4 6 8 10 12 1 7 9 5 7 9 11 3 5 This chain is longer with This chain is 10 Cs long. 12 Cs so we pick this one.

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 4 3 = a central carbon position 4 2 These two branches are 5 3 1 3 equivalent in length, but 6 the lower one is chosen 3 1 5 4 2 2 4 These two branches are equivalent because it has more 1 3 5 2 and because they are longest must branches on it. It must 4 4 3 6 be part of the longest chain. Either also be part of the longest 3 chain. 4 one can be used. 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 11 12 R on C 1 3 R on C4 10 9

R 9 7 3 1 R 4 6 8 10 12 6 5 4 5 7 9 11 8 2

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.

C3 substitution is lower than C4 substitution 11 12 10 The direction of the numbering is reversed because the new branch would get R 9 7 5 3 1 a lower number, C3, at the first point of differnece, than C4 if the numbering 8 6 4 2 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).

11 12 substituents 10 3-methyl There are two one carbon branches on C3 and C9 carbons 8 8-ethyl 9 7 5 3 1 and two two carbon branches, both on the C8 carbon. The 6 4 2 8-ethyl 9-methyl 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 1 C branch = methyl 7 C branch = heptyl 2 C branch = ethyl 8 C branch = octyl 3 C branch = propyl 9 C branch = nonyl 4 C branch = butyl 10 C branch = decyl 5 C branch = pentyl 11 C branch = undecyl 6 C branch = hexyl 12 C branch = dodecyl

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).

11 12 number of identical numerical 10 substituents prefix 2 di- 8 9 1 3 tri- 7 5 4 3 6 2 4 tetra- 5 prnta- 6 hexa- 7 hepta- 8,8-diethyl-3,9-dimethyldodecane etc.

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.

7-butyl Number from the right because 9-propyl the first branch appears at C . These two branches are 2 5-methyl equivalent in length, but 2-methyl the lower one is chosen 10 because it has more 8 2 9 7 5 3 These two branches are equivalent. branches on it. 12 11 4 6 Either one can be used. 1 10-methyl 8,8-diethyl 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 7-butyl-8,8-diethyl-2,5,10-trimethyl-9-propyldodecane 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 4' =part of the longest chain 2'' 3' 5-(2-methylpropyl) 3' 1' = point of attachment to longest chain 2'' 1'' 2' 3' 1' 7-(1-ethylbutyl) 2' 1'' 1'' = point of attachment to longest branch chain 1' 1' 10 8 2 1' Outside the parentheses the numerical prefix does not 8-(1,2-dimethylpropyl) 9 5 3 1211 7 6 4 count for alphabetical order, but inside the parentheses 9-propyl 2' the numerical prefix does count for alphabetical order. 1' 1 If you do not write these prefix names in the correct order, 1'' 1' 3' parent chain = dodecane your structure will still be drawn correctly from the given 1'' 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 Number of Identical Complex Branches bis- 2 tris- 3 tetrakis- 4 pentakis- 5 hexakis- 6 etc.

1' 2' 2 1 5 7 3 1' 2 4 6 10 2' 1 8 3 9 6 4 5

4,4,5,7-tetrakis(1-methylethyl)decane 1,4-bis(1,1-dimethylethyl)

5 Lecture 8 Examples

2 1 CC CC CC Rule 1 - The longest chain is six carbons. 3 1 2 C C CCC C C CCC C C CCC Rule 2 - Number from the end closer to the 3 3 21 two two carbon branches, as C3 positions C C C C C C C C C instead of C positions. 6 6 6 4 5 4 5 4 5 4 Rule 3 - Name two carbon branches as 3-ethyl and 3-ethyl. Rule 4 - Use the di prefix since there are two 6 4 664 4 2 1 5 3 5 335 ethyl substituents. 2 2

1 1 There are many ways to get this name in this particular compound. All of the above are: 3,3-diethylhexane

C 2 1 In this example, the parent name would still be hexane CC 6 4 (six carbons long). This would be the only acceptable 3 5 3 C C CCC 2 parent "hexane". The chain would have to be numbered 1 this way because the methyl substituent gets a lower C C C number than any other possibility, 2-methyl. The 6 5 4 3,3-diethyl would come alphabetically before 2-methyl, so would appear first in the name. 3,3-diethyl-2-methylhexane

C 2 1 C CC 6 4 A slight additional modification produces two identical 5 3 parent structures. There is now a complicated branch 2' 1' 3 2 C C CCC 1 (a branch that has a branch) at the C3 position and C C C 1' parentheses are needed. 6 5 4 2' 3-ethyl-2-methyl-3-(1-methylethyl)hexane

Additional Examples 1.

parent = octane C2, C3, C5 substituents = 2,3,5-trimethyl 3 5 C4, C5 substituents = 4.5-dipropyl 2 4 alphabetical = methyl > propyl 1 6 7 8 2,3,5-trimethyl-4,5-dipropyloctane 2. 2' 1' parent = undecane 3 2 C substituent = 2-methyl 1 2 C4 substituent = 4-(2-methylpropyl) 10 8 6 4 2' C5 substituent = 5-(1,1-dimethylethyl) 11 9 7 5 1' 3' 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' 1' parent = dodecane C6 substituent = 6-pentyl 2 C substituent = 6-(1,2-dimethylbutyl) 3 1 6 4 C5 substituent = 5-methyl 4' 2' 5 5' 3' 1' C4 substituent = 4-(1-methylethyl) 6 8 10 12 7 9 11 2' 1' alphabetical = C (dimethylbutyl) > C (methyl) > C (methylethyl) > C (pentyl) 3' 6 5 4 6 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.

o RXCH2 RCH3 1 = Primary carbons have only one carbon group attached to another carbon. The arrows point at examples of primary carbons.

CH3

H3CXCH2 H3C H2CXCH2 H3C CHCH2 X H3C CXCH2

CH3 CH3

o RNH2 1 = Primary amines have only one carbon group attached to a nitrogen. All of the following nitrogen atoms are primary amines. CH3

CH3 NH2 H3C H2CNHCH2 2 H3C CH NH2 H3C C NH2

CH3 CH3

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. RXCH R CH2 2o = Secondary carbons have two carbon groups attached to them. R R The arrows point at examples of secondary carbons. H2C CH2

H2C CH2 H3C CH X CH3CH2CH2CH2CH2 X H3C H2CXCH2 H2CCH2 CH 3 all Cs are 2o R N H 2o = Secondary amines have two carbon groups attached to a nitrogen. All of the following nitrogen atoms are secondary amines. R CH3 H H H H

CH3 N CH3 CH2 N H3C CH N H3C C N CH CH3 CH CH 3 3 CH3 3 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 3o = Tertiary carbons have three carbon groups attached to them. R C X R C H The arrows point at examples of tertiary carbons. R R

CH3 CH CH H2C 3 3 CH H C o H3C C X H3C H2C C H 2 both Cs are 3 C X H C CH3 CH3 2 CH3

R N R 3o = Tertiary amines have three carbon groups attached to a nitrogen. All of the following nitrogen atoms are tertiary amines. R CH3 CH3 CH CH3 CH3 3 CH3 N CH3 CH2 N H3C CH N H3C C N CH CH3 CH CH 3 3 CH3 3 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 4o = Quaternary carbons have four carbon groups attached to them. The arrows point at R C R examples of quaternary carbons. R CH3 H2C CH2 CH3 CH3 C H C CH o H C C CH H C H C C CH 2 2 both Cs are 4 3 3 3 2 3 C H2C CH2 CH3 CH3 CH3

R 4o = Quaternary ammonium ions have four carbon groups attached to a nitrogen. Such a nitrogen has R N R a positive formal charge. Both of the following nitrogen atoms are quaternary ammonium ions. R CH3 CH3 H2C CH2 N

CH3 N CH2CH2CH2CH2CH3 H2C CH2 C CH3 H2C 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

methine, one hydrogen atom is attached, methine is CH = "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.

CH CH CH X 3 2 2 CH3CH2CH2CH2 X CH3CH2CH2CH2CH2 X CH3CH2CH2CH2CH2CH2 X

n-propyl "X" n-butyl "X" n-pentyl "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 CH3 CH H C 3 H C X H C CH2 X H C CH2 CH2 X H C CH2 CH2 CH2 X CH3 CH3 CH3 CH3 CH3 "iso" pattern isopropyl "X" isobutyl "X" isopentyl "X" 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 CH3

H C X HC X CH3 CH X CH3 CH X (CH3)2CH X CH CH CH3 3 3 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.

H CCHCH CH 3 2 3 H3CCHCH 2 CH2 CH3 H3C H2CCHCH 2 CH3 X X X 3-"X" only one type of "sec" 2-"X" position in sec-butyl "X" sec-pentyl "X" is ambiguous

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 CH3 CH3

CH3 C CH3 C X CH3CH2 C X CH3CH2CH2 C X

CH3 CH3 CH3 CH3

"t-" pattern t-butyl "X" tert-pentyl "X" t-hexyl "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 CH3 CH3

CH3 C CH2 CH3 C CH2 X CH3 C CH2 CH2 X CH3 C CH2 CH2 CH2 X

CH3 CH3 CH3 CH3

"neo" pattern neopentyl "X" 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. c. d. e. b. r. f. N(CH3)2 q. g. (CH3)3N

p. h.

(CH3)3C o. (CH3)2CH NHCH3 n. j. i. NH2 l. m. k.

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.

= cyclohexane

=

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 6 3 1 5 1 1-methyl-3-propylcyclohexane incorrect numbering 4 6 priority based on alphbetical order of branch names 4 2 5 3

7 8 9 6 5 3 6 4 1 5-butyl-2-ethyl-1-methylcyclononane incorrect 5 3 2 2 numbering 4 7 9 8 1 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 , that is acceptable.

2 4 6 8 1 3 5 7 3 2 3 4 4 2 1 5 1 5 3-cyclopentyloctane 1-methyl-3-(1-methylethyl)cyclopentane or 1-isopropyl-3-methylcyclopentane 3-cyclohexyl-2,2,3,4,4-pentamethylpentane priority based on alphbetical order of branch names

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 4 6 8 1 3 5 7 9 parent chain numbers: 1, 2, 3, etc. branch chain numbers: 1', 2', 3', etc. 1' 6' 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 No reference term is necessary for the 2 1 Cl 1-chloro or the 2-methyl substituents Br The cis Cl is given higher because of the referencing of the other priority than the trans Cl. Br 3 substituents at those positions. Cl r-1-bromo-1-chloro-c-2-ethyl-2-methyl-t-3-propylcyclobutane 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.) Br a. b. c. d. e.