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Introduction to Alkanes: Methane, Ethane, and Propane. C n H 2 n +2. The Simplest Alkanes. Methane (CH 4 ) CH 4 Ethane (C 2 H 6 )CH 3 CH 3 Propane (C 3 H 8 )CH 3 CH 2 CH 3. bp -160°C. bp -89°C. bp -42°C. Isomeric Alkanes: The Butanes. C 4 H 10. n -ButaneCH 3 CH 2 CH 2 CH 3 - PowerPoint PPT Presentation
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CCnnHH22nn+2+2
Introduction to Alkanes:Methane, Ethane, and Propane
Methane (CH4) CH4 Ethane (C2H6) CH3CH3
Propane (C3H8) CH3CH2CH3
bp -160°Cbp -160°C bp -89°Cbp -89°C bp -42°Cbp -42°C
The Simplest Alkanes
CC44HH1010
Isomeric Alkanes: The Butanes
n-Butane CH3CH2CH2CH3
Isobutane (CH3)3CH
bp -0.4°Cbp -0.4°C bp -10.2°Cbp -10.2°C
Higher n-Alkanes
CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33
nn-Pentane-Pentane
nn-Hexane-Hexane
CHCH33CHCH22CHCH22CHCH22CHCH33
CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33
nn-Heptane-Heptane
The C5H12 Isomers
nn-Pentane-Pentane
CHCH33CHCH22CHCH22CHCH22CHCH33
IsopentaneIsopentane
(CH(CH33))22CHCHCHCH22CHCH33
NeopentaneNeopentane
(CH(CH33))44CC
CC55HH1212
How many isomers?
The number of isomeric alkanes increases as the number of carbons increase.There is no simple way to predict how many isomers there are for a particular molecular formula.
Number of Constitutionally Isomeric Alkanes
CH4 1 C2H6 1 C3H8 1 C4H10 2 C5H12 3 C6H14 5 C7H16 9
C8H18 18 C9H20 35 C10H22 75 C15H32 4,347 C20H42 366,319 C40H82 62,491,178,805,831
Systematic NomenclatureSystematic Nomenclature
International Union of Pure and Applied Chemistry
IUPACCommittee on Organic Nomenclature
The alkanes The alkanes Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)
Pentane (C5H12)
Hexane (C6H14)
Heptane (C7H16)
Octane (C8H18)
Nonane (C9H20)
Decane (C10H22)
CH4
CH3 CH3
CH3 CH2 CH3
CH3 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
Nomenclature of the AlkanesNomenclature of the Alkanes
Alkanes always have the ending -ane.Side chains (substituents) are named as
alkyl groups.
Common alkyl groupsCommon alkyl groups (C (C11 through C through C44))
CH3
CH3 CH2
CH3 CH2 CH2
CH3 CH2 CH2 CH2
Methyl
Ethyl
Propyl
Butyl
Isopropyl
Isobutyl
(1-Methylethyl)
(2-Methylpropyl)
sec-Butyl(1-Methylpropyl)
tert-Butyl(1,1-Dimethylethyl)
CH3 CH
CH3
CH3 CH CH2
CH3
CH3 CH2 CH
CH3
CH3 C
CH3
CH3
IUPAC nomenclature of alkanesIUPAC nomenclature of alkanes
identify the longest chain -- parent number from the end closest to first branch Name the groups attached to the chain, using the
carbon number as the locator. Alphabetize substituents. Use di-, tri-, etc., for multiples of same substituent combine number and name of substituent with
parent name, separating with hyphen
Longest Chain The number of carbons in the longest chain
determines the base name: ethane, hexane. If there are two possible chains with the
same number of carbons, use the chain with the most substituents.
C
CH3
CH2
CH3
CH CH2 CH2 CH3
CH CH2 CH3H3C
H3C
=>
Number the Carbons Start at the end closest to the first attached
group. If two substituents are equidistant, look for
the next closest group.
1
2
3 4 5
6 7CHH3C
CH3
CH
CH2CH3
CH2 CH2 CH
CH3
CH3
CH3 CH2 CH CH3
CH3
Organic nomenclatureOrganic nomenclature
4 3 2 1
2-methylbutane
CH3 CH2 CH CH3
CH2 CH3
Find the longest continuousFind the longest continuouscarbon chaincarbon chain
1 2 3
4 5
3-methylpentane
CH3 CH2 CH CH2 CH2 CH3
CH2 CH2 CH3
You must choose the longestYou must choose the longestcontinuous carbon chaincontinuous carbon chain
4 3 2 1
5 6 7
4-ethylheptane
IUPAC rules
1. Find the longest straight chain = parent chain
2. Number the parent chain in the direction that gives the lowest number to the substituents at the first point of difference.
3. Two or more identical groups are indicated by di, tri, tetra, etc.
CH3 CH2 CH2 CH2 CH
CH2 CH3
CH3Longest chain is 7 (not 6).This is 3-methylheptane.
.
2,3,6-trimethylheptane (not 2,5,6-trimethyl heptane)
2,2,6,6,7-pentamethyloctane (not 2,3,3,7,7-pentamethyloctane)
4. Different groups are listed in alphabetical order (di, tri, tetra, etc. don’t count; n, sec, tert don’t count; iso does).
5. If the numbering is the same in both directions, choose the numbering to follow the alphabetical order.
IUPAC rules
6-ethyl-5-isopropyl-2,2-dimethyloctane
5-ethyl-6-methyldecane
6. When two or more chains compete for the longest, the choice goes to the one with the greater number of side groups.
IUPAC rules
2,4,6-trimethyl-5-propyloctane
CH3 CH2 CH2 CH CH CH2 CH3
CH3
CH2 CH3
Number from the end nearestNumber from the end nearestthe first substituentthe first substituent
7 6 5 4 3 2 1
4-ethyl-3-methylheptane
CH3 CH2 CH2 CH CH2 CH CH2 CH3
CH2 CH3
CH3
Number from the end nearestNumber from the end nearestthe first substituentthe first substituent
8 7 6 5 4 3 2 1
3-ethyl-5-methyloctane
CH3 CH CH CH3
CH3
CH3
Use “di-” with two substituentsUse “di-” with two substituents
1 2 3 4
2,3-dimethylbutane
CH3 CH2 C CH2 CH2 CH3
CH3
CH3
Every substituent must get a numberEvery substituent must get a number
1 2 3 4 5 6
3,3-dimethylhexane
CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3
CH3CH3
CH3
Number from the end nearestNumber from the end nearestfirst substituentfirst substituent
10 9 8 7 6 5 4 3 2 1
2,7,8-trimethyldecane
CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3
CH3
CH3
CH3
Number from the end which hasNumber from the end which hasthe “first difference”the “first difference”
1 2 3 4 5 6 7 8 9 10
3,4,8-trimethyldecane
CH3 CH CH2 C CH3
CH3 CH3
CH3
A More-Highly-SubstitutedA More-Highly-SubstitutedCarbon Takes PrecedenceCarbon Takes Precedence
5 4 3 2 1
2,2,4-Trimethylpentane
CH3 CH2 CH CH2 CH2 CH CH2 CH3
CH3 CH2 CH3
Which end do we number from?Which end do we number from?
8 7 6 5 4 3 2 1
3-ethyl-6-methyloctane
IUPAC rules
6-ethyl-2,2,5,7-tetramethylnonane (not 6,7-diethyl-2,2,5-trimethyloctane.
7-tert-butyl-8-isobutyl-4-isopropyldodecane(hyphenated words aren’t alphabetized).
OR7-(1,1-dimethylethyl)-4-(1-methylethyl)-8-(2-methylpropyl)dodecane
Name the following compounds.
CH2CH2
CH2CH
CH2CH3 C
CH2CH2
CH2CH2
CH2CH3
CH3
CCH3 CH2
CH3 CH2 CH3
CH3
Good Luck!Good Luck!
7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane
Branched Substituents
isopropyl
sec-butyl
CH3 CH CH2
CH3
CH2 CH
CH3
CH3 CH3 C CH3
CH3
CH3 CH CH3
isobutyl tert-butyl(t-butyl)
CH3 C CH3
CH2
CH3
neo-pentyl
Halogens and other side groups Fluoro –F Chloro –Cl Bromo –Br Iodo –I Nitro –NO2 N
O
O
CH3 CH2 Br
Bromoethane
“Ethyl bromide”
CH3 C Cl
CH3
CH3
2-Chloro-2-methylpropane
“tert-Butyl chloride”
CH3 CH CH CH2 CH3
Br CH3
2-Bromo-3-methylpentane
Complex Substituents If the branch has a branch, number the
carbons from the point of attachment. Name the branch off the branch using a
locator number. Parentheses are used around the complex
branch name.1
2
31-methyl-3-(1,2-dimethylpropyl)cyclohexane =>
The isopropyl group can be named The isopropyl group can be named as a “complex” substituentas a “complex” substituent
1-methylethyl
CH3 CH
CH3
2 1
If you can name this,If you can name this,you can name almost anything!you can name almost anything!
1 2 3 4 5 6
7
8 9
4-isopropyl-2,6,6-trimethylnonane
CH3 CH CH2 CH CH2 C CH3
CH3
CH
CH3
CH3
CH3
CH2
CH2 CH3
Now, rename the isopropyl group. Now, rename the isopropyl group. Notice the alphabetical order!Notice the alphabetical order!
1 2 3 4 5 6
7
8 9
2,6,6-trimethyl-4-(1-methylethyl)nonane
CH3 CH CH2 CH CH2 C CH3
CH3
CH
CH3
CH3
CH3
CH2
CH2 CH3
Naming complex substituents -- Naming complex substituents -- this one is alphabetized under dthis one is alphabetized under d
1,3-dimethylbutyl
CH3 CH CH2 CH
CH3CH3
4 3 2 1
deciding on alphabetical order deciding on alphabetical order for complex groupsfor complex groups
Complex groups are alphabetized under the first letter of the name
(1,3-dimethylbutyl) = d(1,1,2-trimethylpropyl) = t(1-ethyl-1,2-dimethylbutyl) = e
Naming complex substituentsNaming complex substituents
2-ethyl-1,1-dimethylbutyl
CH3 C CH CH2 CH3
CH3 CH2 CH3
1 2 3 4
CH3 CH2 CH2 CH2 C CH2 CH2 CH2 CH3
C
CH2 CH2 CH3
CH3
CH2CH2 CH3CH3
This Should Be FunThis Should Be Fun
1 2 3
1 2 3 4 5 6 7 8 9
5-(1-Ethyl-1-methylpropyl)-5-propylnonane
CH2CH2
CH2CH
CH2CH3 C
CH2CH2
CH3
CH2CH3
CH3
CCH3 CH3
CH3
name this two ways -- name this two ways -- (the complex group)(the complex group)
7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane7-tert-butyl-3-ethyl-7-methyldecane
Common Nomenclature Common Nomenclature PitfallsPitfalls
Did not find the longest carbon chainNumbered chain from the wrong endForgot to repeat number for each identical
substituent; forgot to use di- tri- tetra-, etc.Used “iso”, “sec”, or “tert” as part of a parent name
Confusing propyl / isopropyl, etc.Writing the name as more than one wordIncorrect punctuation
degree of substitutiondegree of substitutionCH3 R R CH2 R
R CH R
R
R C R
R
R
primary (1°) secondary (2°)
tertiary (3°) quaternary (4°)
CH3 CH CH2 CH CH2 C CH3
CH3
CH
CH3
CH3
CH3
CH2
CH2 CH3
Degree of SubstitutionDegree of Substitution
1° 1°
1° 3° 2° 3° 2° 4° 1°
1° 3° 2°
1° 2° 1°
LOCANT PREFIX N STEM SUFFIX
numbers substituents number -ALK(AN)- ending
Block diagram for Block diagram for nomenclaturenomenclature
cyclic moleculescyclic molecules
CC
C
H H
H
H
H
H
CH2
CH2
CH2
Cyclopropane
C
C C
C
H
H
H
H
H
H
H
H
CH2
CH2 CH2
CH2
Cyclobutane
C
CC
C
C
H HH H
HH
HH
HHCH2
CH2
CH2
CH2
CH2
Cyclopentane
C
CC
C
CC
H HH
H
H
H
HH
H
H
H
HCH2
CH2CH2
CH2
CH2
CH2
Cyclohexane
Nomenclature for Cyclic Alkanes For compounds with a single ring, add the
prefix “cyclo-” to the root name for the alkane comprising the ring.
Nomenclature of the Substituted Nomenclature of the Substituted CycloalkanesCycloalkanes
If there is only one substituent, do not use the “1”. If there is more than one substituent, you must use all
numbers, including “1”! Number around the ring in a direction to get from the first
substituent to the second substituent by the shorter path. For equivalent degrees of substitution, number in a
direction that follows the alphabetical sequence. A carbon with greater substitution has precedence in
numbering.
Br
Bromocyclopropane
CH3
CH3
1,1-Dimethylcyclohexane
CH3
CH3
CH2CH3
4-Ethyl-1,1-dimethylcyclohexane
Two ways of naming thisTwo ways of naming this
1-isopropyl-2-methylcyclohexane1-methyl-2-(1-methylethyl)cyclohexane
CH3
CH
CH3
CH3
Numbering Starts at the Most Numbering Starts at the Most Highly-Substituted CarbonHighly-Substituted Carbon
Cl CH3
CH3
CH3
2 13 74 6 5
2-Chloro-1,1,6-trimethylcycloheptane
cycloalkyl groupscycloalkyl groups
Cyclopropyl Cyclobutyl
Cyclopentyl Cyclohexyl
C
CH3
CH2CH2CH3 CH3
3-Cyclobutyl-3-methylpentane
CH3 CH2 CH CH3
2-Cyclobutylbutanesec-Butylcyclobutane
Name the following cycloalkanes. Check your answers by clicking on the arrow.
IUPAC rules
1,1,2-trimethycyclohexane
4-cyclopentyl-2,3-dimethylhexane
1,2-dicyclopropylethane