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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 -Butane CH 3 CH 2 CH 2 CH 3
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Introduction to Alkanes:Methane, Ethane, and Propane CnH2n+2
The Simplest Alkanes • Methane (CH4) CH4 • Ethane (C2H6) CH3CH3 • Propane (C3H8) CH3CH2CH3 bp -160°C bp -89°C bp -42°C
n-Butane CH3CH2CH2CH3 • Isobutane (CH3)3CH bp -0.4°C bp -10.2°C
CH3CH2CH2CH2CH3 n-Pentane CH3CH2CH2CH2CH2CH3 n-Hexane CH3CH2CH2CH2CH2CH2CH3 n-Heptane
C5H12 (CH3)2CHCH2CH3 CH3CH2CH2CH2CH3 Isopentane n-Pentane (CH3)4C Neopentane
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 Nomenclature • International Union of Pure and Applied Chemistry • IUPAC • Committee on Organic Nomenclature
Nomenclature of the Alkanes • Alkanes always have the ending -ane. • Side chains (substituents) are named as alkyl groups.
IUPAC 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.
1 3 4 5 2 6 7 Number the Carbons • Start at the end closest to the first attached group. • If two substituents are equidistant, look for the next closest group.
Organic nomenclature 4 3 2 1 2-methylbutane
Find the longest continuouscarbon chain 1 2 3 4 5 3-methylpentane
You must choose the longestcontinuous 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. Longest 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)
IUPAC rules 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. 6-ethyl-5-isopropyl-2,2-dimethyloctane 5-ethyl-6-methyldecane
IUPAC rules 6. When two or more chains compete for the longest, the choice goes to the one with the greater number of side groups. 2,4,6-trimethyl-5-propyloctane
Number from the end nearestthe first substituent 7 6 5 4 3 2 1 4-ethyl-3-methylheptane
Number from the end nearestthe first substituent 8 7 6 5 4 3 2 1 3-ethyl-5-methyloctane
Use “di-” with two substituents 1 2 3 4 2,3-dimethylbutane
Every substituent must get a number 1 2 3 4 5 6 3,3-dimethylhexane
Number from the end nearestfirst substituent 10 9 8 7 6 5 4 3 2 1 2,7,8-trimethyldecane
Number from the end which hasthe “first difference” 1 2 3 4 5 6 7 8 9 10 3,4,8-trimethyldecane
A More-Highly-SubstitutedCarbon Takes Precedence 5 4 3 2 1 2,2,4-Trimethylpentane
Which end do we number from? 8 7 6 5 4 3 2 1 3-ethyl-6-methyloctane
IUPAC rules Name the following compounds. 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). OR 7-(1,1-dimethylethyl)-4-(1-methylethyl)- 8-(2-methylpropyl)dodecane
Good Luck! 7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane
Branched Substituents isopropyl sec-butyl isobutyl tert-butyl (t-butyl) neo-pentyl
Halogens and other side groups • Flouro –F • Chloro –Cl • Bromo –Br • Iodo –I • Nitro –NO2
Bromoethane “Ethyl bromide”
2-Chloro-2-methylpropane “tert-Butyl chloride”
1 2 3 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-methyl-3-(1,2-dimethylpropyl)cyclohexane =>
The isopropyl group can be named as a “complex” substituent 1-methylethyl
If you can name this,you can name almost anything! 1 2 3 4 5 6 7 8 9 4-isopropyl-2,6,6-trimethylnonane
Now, rename the isopropyl group. Notice the alphabetical order! 1 2 3 4 5 6 7 8 9 2,6,6-trimethyl-4-(1-methylethyl)nonane
Naming complex substituents -- this one is alphabetized under d 1,3-dimethylbutyl
deciding on alphabetical order for 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 substituents 2-ethyl-1,1-dimethylbutyl