ch3(3)-aklanes&cycloaklanes
TRANSCRIPT
Alkanes and Cycloalkanes
Structure FormsC3H8
Kekul or Wedge/dash
H3C CH2 CH3skeletal
H H
H
H
H
CH3CH2CH3condensed
H H H
2
Classes of HydrocarbonsOrganic Compounds
hydrocarbons (C,H)
heteroatomic (O, N, P, S, X, etc.)
aliphatic (fatty)
aromatic (pleasant smelling)
alkane C C
alkene C C
alkyne C C
cyclic
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Functional Groups
A functional group is an atom or group of atoms that have a characteristic chemical behavior. The chemistry of every organic molecule, regardless of size and complexity, is determined by the functional groups it contains.
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Functional Groups
O C H3 C O O C O5
H
Types of Functional Groups: Multiple CarbonCarbon Bonds
Alkenes have a C-C double bond Alkynes have a C-C triple bond Arenes have special bonds that are represented as alternating single and double C-C bonds in a sixmembered ring6
Functional Groups
Alkyl halideH H C H H C H H C H H C H Br
R-X where X is any halogen X7
Functional Groups
AlcoholsH H C H H C H H C H H C H OH
R-OH where R is any alkyl group8
Functional Groups
EthersH H C H H C H H O C H H
R-O-R where R is any alkyl group9
Functional Groups
Aldehydes
H O H C H10
C H
Functional Groups
Ketone
H O H H C C C H
H H Propanone (acetone)11
Functional Groups
Carboxylic acids
H O H C HEthanoic acid (acetic acid)12
C OH
Functional Groups
Ester
H H C H
O C O CH3
Methyl ethanoate (methyl acetate)13
Functional Groups
Amine
H H C HMethylamine
NH2
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Functional Groups
Amide
O H3 C C NH2Ethanamide (acetamide)15
Functional Groups
Acid anhydride
O H3 C
O CH3
C O C
Ethanoic anhydride16
Functional Groups
Acid halide
O H3 C C ClEthanoyl chloride17
Functional Groups
Nitro
O H3 C N O18
Nitromethane
Functional Groups
Arene
benzene19
Functional Groups
Halide
H3 C
Cl
Chloromethane20
Functional Groups
Nitrile
H3 C
C N
Ethanenitrile
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Functional Groups
Sulfide
H3 C
S
CH3
22
Functional Groups
Thiol
H3 C
S
H
Methanethiol
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Functional GroupsO OCH3 O N H HO O24
NH2
Alkanes and Alkane Isomers
Alkanes: Compounds with C-C single bonds and C-H bonds only (no functional groups) Connecting carbons can lead to large or small molecules The formula for an alkane with no rings in it must be CnH2n+2 where the number of Cs is n Alkanes are saturated with hydrogen (no more can be added They are also called aliphatic compounds
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AlkanesH3C CH2 CH2 CH3 H H H H H C C C C H H H H H CH3CH2CH2CH3 H C H H C H H CH3(CH2)2CH3
H H C H
H C H
CH3CH(CH3)CH2CH326
Structure
Shape
tetrahedral about carbon all bond angles are approximately 109.5
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Alkane Isomers
CH4 = methane, C2H6 = ethane, C3H8= propane The molecular formula of an alkane with more than three carbons can give more than one structure C4 (butane) = butane and isobutane C5 (pentane) = pentane, 2-methylbutane, and 2,2dimethylpropane Alkanes with Cs connected to no more than 2 other Cs are straight-chain or normal alkanes Alkanes with one or more Cs connected to 3 or 4 Cs are branched-chain alkanes
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Alkanes
straight chain or normal alkanesH H H H C C H H H H H H H C C C H H H H H H H H H C C C C H H H H H
H C H H
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Alkanes
branched chains
H H H H H H H H C C C C C H H H H H H H C H H H H H C C C C H H H H H H C H H H H C C C H H H H C H H30
Branching vs. No Branching
There are 2 isomeric butanes
n-butane
H H C H
H C H
H C H
H C H H
C4H10
n means normal or in a straight chainH H H H C H C C H H H C H H31
isobutane
C4H10
Find the Isomers of C5H12
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Find the Isomers of C6H14Draw the structures for C6H14 starting with the longest chain (6 in a row) H H H H H HH C H C H C H C H C H C H H
next draw all structures with 5 carbons in the longest chain (substitute for the H s)then substitute for other H sH H C H H H H C C C H H H H C H H C H H33
Find the Isomers of C6H14
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Find the Isomers of C7H16
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Isomers
Same chemical formula, but different structure.
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Constitutional Isomers
Isomers that differ in how their atoms are arranged in chains are called constitutional isomers Compounds other than alkanes can be constitutional isomers of one another They must have the same molecular formula to be isomers
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Constitutional IsomerismMolecular Cons titutional Formula Isomers CH 4 C 5 H12 C 10 H22 C 15 H32 C 30 H62 1 3 75 4,347 4,111,846,76338
World population is about 6,000,000,000
Names of Small HydrocarbonsNo. of Carbons 1 2 3 4 5 6 7 8 9 10 Formula Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane (CnH2n+2) CH4 C 2H 6 C 3H 8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H2239
Alkyl Groups
Alkyl group remove one H from an alkane (a part of a structure) General abbreviation R (for Radical, an incomplete species or the rest of the molecule) Name: replace -ane ending of alkane with -yl ending
CH3 is methyl (from methane) CH2CH3 is ethyl from ethane
See Table 3.4 for a list
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Types of Alkyl groups
Classified by the connection site (See Figure 3.3) a carbon with one carbon attached to it (primary alkyl group) a carbon with two carbons attached to it (secondary alkyl group) a carbon with three carbons attached to it (tertiary alkyl group) a carbon with four carbons attached to it (quaternary alkyl group)
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Types of Alkyl groups
Classified by the connection site (See Figure 3.3)
a carbon with one carbon attached to it (primary alkyl group) a carbon with two carbons attached to it (secondary alkyl group) a carbon with three carbons attached to it (tertiary alkyl group) a carbon with four carbons attached to it (quaternary alkyl group)
CH3
CH3 CH3 CH3 C CH2CH C CH3 CH3 CH3
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Degree of Substitution
CH31 3
2
4 CH 3
CH3CHCHCH2CH2C CH3 CH2 CH3 CH343
Nomenclature
International Union of Pure and Applied Chemistry
colloquially: eye-you-pac
Devised following WWII ca. 1946-1950
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Naming Alkanes
Compounds are given systematic names by a process that uses
Prefix-Parent-Suffix Named as longest possible chain Carbons in that chain are numbered in sequence substituents are numbered at their point of attachment Compound name is one word (German style) Complex substituents are named as compounds would be
Follows specific rules
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Nomenclature Where are substituents? Prefix-Parent-Suffix
How many carbons? What family?International Union of Pure and Applied Chemistry (IUPAC)46
Nomenclature Prefix-Parent-Suffix
CH3 CH2 CH CH2 CH2 CH CH2 CH3 CH33-ethyl-6-methyl
CH2 CH3
octane47
NomenclatureName Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane Undecane Dodecane
Alkanes have the general formula CnH2n+2
Condensed Structure CH4 CH3CH3 CH3CH2CH3 CH3(CH2)2CH3 CH3(CH2)3CH3 CH3(CH2)4CH3 CH3(CH2)5CH3 CH3(CH2)6CH3 CH3(CH2)7CH3 CH3(CH2)8CH3 CH3(CH2)9CH3 CH3(CH2)10CH3
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The Longest Continuous Chain of Carbon AtomsC-C C -C -C -C -C -C -C -C -C Call possibilites must be examined it wont always be the horizontal one as shown here
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try these also ..
C -C C- C-C-C -C-C-C-C-C C C
C -C C-C-C- C-C-C-C-C-C
6
8
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Nomenclature
Parent name of the longest carbon chain is alkane Groups attached to the parent chain are called substituents Each substituent is given a name and a number
If substituent occurs more than once, di-, tri-, tetra-, etc.
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Nomenclature
Number the chain to give the substituent encountered first the lowest number If there are different substituents, list them in alphabetical order. The following are not included in alphabetization.
di-, tri-, tetra-, etc. hyphenated prefixes, such as sec- and tert-
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Nomenclature
Alkyl groups
Propyl Isopropyl Butyl Isobutyl sec-butyl tert-butyl
-CH2CH2CH3 -CHCH(CH3)2 -CH2CH2CH2CH3 -CH2CHCH(CH3)2 -CH(CH3)CH2CH3 -C(CH3)3
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Nomenclature
Alkyl groupsName pentyl isopentyl Condens ed Structural Formula -CH 2 CH2 CH 2 CH 2 CH 3 -CH 2 CH2 CHCH3 CH 3 CH3 neopentyl -CH 2 CCH 3 CH353
Nomenclature
Find the longest chain.
CH 2 CH 3 CH3CH2CH2CH CH3CH3 CH2 H3C CH CH CH2CH 3 CH2CH 2CH3
hexane
heptane
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Nomenclature
If two different chains of equal length are present, choose the one with the larger number of branch points.
CH3 CH3CHCHCH2CH2CH3 CH2 CH355
Nomenclature
Number the atoms in the main chain:
Begin at the end nearer the first branch point (lower number).1 2
CH3 CH23 4
H 3C
CH CH CH2 CH3 CH2 CH2 CH35 6 756
Nomenclature
If branching is equal distant away from both ends of the parent chain, begin at the end nearer the second branch point.
H3C CH2 CH3 CH3CHCH 2CH2CHCHCH2CH3 CH2 CH357
Nomenclature
Identify the number of substituents:
Assign a number to each substituent according to its point of attachment to the main chain.
3-ethyl 9 8 4-methyl H3C CH2 CH3 3 7-methyl CH3CHCH2CH2CHCHCH2CH3 7 6 5 4 CH2 CH3 2 1
3-ethyl-4,7-dimethylnonane
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Nomenclature
If there are two substituents on the same carbon, assign them both the same number.
4-ethyl-2,4-dimethylhexane
CH3 CH3 CH3CH2CCH2CHCH3 CH2 CH3
2-methyl 4-methyl 4-ethyl
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Nomenclature
Write the name as a single word, using hyphens to separate the different prefixes and commas, to separate numbers. Use di-, tri-, etc. if more than one identical substituents Dont use these prefixes for alphabetizing purposes.
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Nomenclature3-methylhexane
CH2 CH3 CH3CH2CH2CH CH361
Nomenclature4-ethyl-3-methylheptane
1 CH33 CH 2 CH2 CH 2 4 CH3CHCHCH2CH3 CH 33 CHCHCH 2CH 3 CH2 CH2 CH3 CH 2 CH2 CH 3 6 7 5
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Nomenclature3-ethyl-2-methylhexane
CH3 CH3CHCHCH2CH2CH3 CH2 CH363
Nomenclature
Name a complex substituent and begin numbering at the point of attachment and set it off in parentheses.
CH3 CH3CH CHCH2CH2CH CH2CH CH3 CH3 CH3 CH2CH2CH2CH364
Nomenclature2,3-dimethyl-6-(2-methylpropyl)decane 2-methylpropyl CH3 1CH3CH CHCH2CH2CH CH2CH CH3 CH3 CH3 CH2CH2CH2CH365
2
3
CH 3 CH 3
Nomenclature
CH CHCH 3
1,2-dimethylpropyl
CH 3 CH3 CH 3CH 2CH2CH2CH CH CHCH3 CH 2 CH 3 CH 2 CH CH 3
2-methyl-5-(1,2-dimethylpropyl)nonane66
Nomenclature-Historical
Threecarbon alkyl group:
CHCH3
isopropyl (i-pr)
CH367
Nomenclature-Historical
Fourcarbon groups:
CHCH2CH3 CH3
CH2CHCH3 CH3
CH3 C CH3 CH3
sec-butyl
isobutyl
tert-butyl
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Nomenclature-Historical
Fivecarbon alkyl groups:
CH2CH2CHCH3 CH3isopentyl
CH3 CH2CCH3 CH3neopentyl69
Nomenclature
H 3C CH CH3 H3C CH2 CH 2 CH CH2 CH2CH 34-(1-methylethyl)heptane or 4-isopropylheptane
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If you can name this, you can name anything!CH31 2 3 4 5 6
CH3 CH3
CH3 CH CH2 CH CH2 C CH3 CH 7 CH3 89
CH2 CH2 CH371
4-isopropyl-2,6,6-trimethylnonane
How about this?CH3
CH3CH22-cyclobutyl-5-methylhexane not (1,4-dimethylpentyl)cyclobutane
CH3
CH3
5-ethyl-1,1,3-trimethyl-2-(2methylpentyl)cyclohexane72
Properties of Alkanes
Called paraffins (low affinity compounds) because they do not react as most chemicals They will burn in a flame, producing carbon dioxide, water, and heat They react with Cl2 in the presence of light to replace Hs with Cls (not controlled)
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Physical Properties
Boiling points and melting points increase as size of alkane increases Forces between molecules (temporary dipoles, dispersion) are weak
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Alkane MP & BP Trends
The dependence of the boiling and melting points on chain length can be explained in terms of increasing attractive van der Waals interactions as the chain length increases.
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Cycloalkanes
Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes rings of CH2 units, (CH2)n, or CnH2n Structure is shown as a regular polygon with the number of vertices equal to the number of Cs (a projection of the actual structure)
cyclobutane cyclopropane cyclopentane cyclohexane76
Cycloalkanes
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CycloalkanesCH2OH CO H3C OH H O Hcortisone78
O H3C
Cycloalkanes
Structure and nomenclature
to name, prefix the name of the corresponding openchain alkane with cyclo-, and name each substituent on the ring if only one substituent, no need to give it a number if two or more substituents, number from the substituent of lowest alphabetical order where there is choice, number to give substituents the lowest set of numbers
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Naming Cycloalkanes
Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible. Number the substituents and write the name
if only one substituent, no need to give it a number
See text for more details and examples
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Nomenclature
For alkyl-substituted cycloalkanes, start at the point of attachment and number the substituents on the ring so as to arrive at the lowest sum.CH 31 6 5 4 2 3
1,3-dimethylcyclohexane not 1,5-dimethylcyclohexaneCH 381
Nomenclature
Halogens are treated exactly like alkyl groups.1-bromo-3-ethyl-5-methylcyclohexane Br CH33 4 2 1
Br
CH3CH2
CH 382
1-bromo-2-methylcyclobutane
Cis-Trans Isomerism in Cycloalkanes
Rotation about C-C bonds in cycloalkanes is limited by the ring structure Rings have two faces and substituents are labeled as to their relative facial positions There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite sides (trans)
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Stereoisomers
Compounds with atoms connected in the same order but which differ in three-dimensional orientation, are stereoisomers The terms cis and trans should be used to specify stereoisomeric ring structures Recall that constitutional isomers have atoms connected in different order
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Cis-Trans IsomerismH3 C CH3
H3 C CH3
cis-1,2-dimethylcyclopropane trans-1,2- dimethylcyclopropane
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Cis-trans isomerism
1,2-dimethylcyclopentane
H H H
H H H
H
H H H
H
H CH3 H
H CH3 CH3 cis-1,2-dimethylcyclopentane
H
CH3 H trans-1,2-dimethylcyclopentane
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Cis-trans isomerism
1,4-Dimethylcyclohexane
planar hexagon representationsH CH3 H H
H H3 C trans -1,4-Dimethylcyclohexane
H3 C CH3 cis -1,4-Dimethylcyclohexane
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