Post on 07-Apr-2018
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Hydro Carbon Organic Chemistry
Organic Chemistry is the study of covalent compounds which contain carbon.
ex: CH4, C8H18, C6H12O6, CCl2F2
There are more carbon-containing compounds than all other types of compounds put together,
making up more than half of all known compounds. Why carbon?
Carbon is able to bond with other carbon atoms, to form chains, rings, spheres and sheetsof almost any size (no other element is so versatile).
Carbons tetravalence (four bonding sites) enable it to form branched chains, and single,
double or triple bonds.
Organic compounds do not include:
most common ionic compounds containing carbon (ex: CO32-, C2H3O2
-, CN-)
oxides of carbon (CO, CO2)
I. Hydrocarbons
Compounds containing only C and H 2 types of hydrocarbons:
(1) aliphatic hydrocarbons do not contain benzene rings
(2) aromatic hydrocarbons contain benzene rings or similar structures
saturated vs. unsaturated hydrocarbons
saturated hydrocarbons contain only single bonds (no double or triple bonds)
unsaturated hydrocarbons have one or more double or triple bonds
homologous series a set of compounds whose nearest neighbors differ by one repeating
unit, most often a methylene group ( CH2 )
straight-chain alkanes: CnH2n+2
straight-chain alkenes: CnH2n straight-chain alkynes: CnH2n-2
Members of a homologous series have similar chemical properties (they undergo similar
reactions), and have a gradation in physical properties (such as melting and boiling point.).
The boiling points of alkanes gradually increases as the number of carbons increases.
Plotting the boiling point against chain length (# of carbon atoms) gives a steep graph at
first, but flattens later (refer to attached graph/data table).
In other words, the bigger the molecule, the higher the melting and boiling points.
Hydrocarbons are effectively non-polar because of the symmetry of the molecules and
the very low polarity of the C H bond (an electronegativity difference of 0.4 means it is
effectively a non-polar bond).
Thus, the only intermolecular forces acting on hydrocarbons are London Dispersionforces.
Larger molecules have more surface area, so more attractive forces exist between
molecules, requiring more energy to separate them, resulting in higher boiling points.
In general, chain-branching causes a slight decrease in boiling point, compared to the
straight-chain compound with the same number of carbons. This is because the molecule
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becomes more compact, with a smaller surface area, reducing the intermolecular
attractions.
I. a. Alkanes(also calledparaffins)
hydrocarbons containing onlysingle bonds (they are all saturated)
alkanes have the general formula CnH2n+2
name formula structural formula structural isomers
methane CH4
ethane C2H6
propane C3H8
butane C4H10
pentane C5H12
hexane C6H14
heptane C7H16
octane C8H18
nonane C9H20
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decane C10H22
all alkanes end in -ane
structural isomers compounds with the same molecular formula, but different structural
formula (i.e. same # of Cs and Hs but theyre arranged differently)
examples:
Pentane 2-Methylbutane
Naming alkanes Rules for nomenclature:
1) Find the longest continuous (though not necessarily straight) chain of carbon atomsYou name the hydrocarbon based on this longest chain.
2) Any carbon chain branching off from the longest chain is named as alkyl group
Alkyl group use the same prefixes, replacing ane with yl
3) Each carbon must have a number. Carbons are numbered in the direction giving the
lowest possible number for all alkyl groups (substituents).
4) When there is more than one of thesame alkyl group, use prefixes like di-, tri-, tetra,
penta-, etc. and identify the # of the carbon(s) on which they are found
Use the lowest possible numbers!
Position #s are separated by commas, and are followed by a hyphen.
5) When there are 2 are more differentalkyl groups, put them in alphabetical order precededby their position number.
methylbutane 2,3-dimethlypentane 3-ethyl-2-methylpentane
(2-methylbutane)
(you dont need to use a number prefix
if no other position is possible)
Alkanes are relatively unreactive due to the inertness of the C-H and C-C bonds.
The inertness of the C-H and C-C bonds is due to 2 main factors:
1. low bond polarity there is little to no difference in electronegativity between the
bonded atoms (C = 2.5, H = 2.1 effectively a non-polar covalent bond)
2,2-Dimethylpropane
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2. high bond energy these bonds are very short and thus very difficult to break
Alkane m.pt. / C b.pt. / C
CH4 -183 -162
C2H6 -172 -88C3H8 -188 -42
C4H10 -138 0
C5H12 -130 36
C6H14 -95 69
C7H16 -91 98
C8H18 -57 126
C9H20 -54 151
C10H22 -30 174
C11H24 -26 196
C12H26 -10 216
C13H28 -5 235
C14H30 6 254
C15H32 10 271
C16H34 18 287
C17H36 22 302
C18H38 28 317
C19H40 32 331
C20H42 36 344
Figure 2.1: Melting and Boiling Points of Straight-Chain Alkanes
Figure 2 .2: Bo iling Points of Straight-Chain Alkane
-200
-100
0
100
200
300
400
0 4 8 12 16 20
Number of Carbon Atom
Temperature/deg.
C
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Isomers compounds with the same molecular formula but differentstructural formula
Draw and name all the isomers with a molecular formula C5H12
Alkyl group (Side Groups) a hydrocarbon group that is attached tothe parent chain of a molecule
Alkyl groups to know and love!!
Methyl Ethyl
Propyl (n-propyl) isopropyl
Butyl (n-butyl) s-butyl (secondary butyl)
Isobutyl t-butyl (tertiary butyl)
Cycloalkanes cycloalkanes alkanes in which the carbon atoms form a ring
The general formula for cycloalkanes is CnH2n
examples:
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cyclopropane cyclobutane cyclopentane cyclohexane
naming cycloalkanes:
1) Use the prefix cyclo- before the number of carbons in the ring.
2) Single substituents do not need to be numbered, since all positions are equivalent.
3) When there is more than one of thesame functional group, use prefixes like di-, tri-, tetra,penta-, etc. and identify the # of the carbon(s) on which they are found.
Use the lowest possible numbers!
Position #s are separated by commas, and are followed by a hyphen.
4) When there are 2 or more differentalkyl groups, put them in alphabetical order precededby their position number.
examples:
1,1-dimethylcyclopentane 1-ethlymethylcyclobutane propylcyclohexane
I. b. Alkenes(also called olefins)
hydrocarbons which contain at least one double bond
alkenes have the general formula CnH2n
examples:
name formula structural formula
ethene C2H4
propene C3H6
(you dont need to use a number
prefix if no other position is possible)
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butene C4H8
(1-butene)
2-butene C4H8
2-methylpropene C4H8
all alkenes end in -ene
Naming alkenes
When naming alkenes, find the longest chain containing a double bond.
Carbon atoms of the longest chain are numbered from the end closest to the double bond.(i.e. assign each carbon in the longest chain a number, such that the double bond occurs
on the carbon with the lowest possible number)
The position number of the double bond is assigned to the first carbon atom of the double
bond (i.e. the lowest possible number carbon).
ex 1:
2-pentene
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ex 2:
3-heptene
If there is more than one double bond, use prefixes (di-, tri-, etc.) immediately before the
ene to indicate the number of double bonds, and use numbers separated by commas to
indicate their positions (again, number the carbons so that the first double bond is at the
lowest possible position).
ex 1:
1,4-hexadiene
ex 2:
Rules for naming alkyl groups attached to alkenes are similar to the rules for alkanes, with
the following difference:
The double bond takes precedence! Number the carbons so that the double bond occurs
at the lowest possible number carbon. Position numbers for alkyl groups thus depend onthe number assigned to the double bond.
Bond length and bond energy are inversely related.
The shorter the bond length, the higher the bond energy:
bond bond length (pm) bond energy (kJ/mol)
CC 154 347
C=C 134 611
C C 121 837
CH 110 414CN 147 293
CCl 176 330CO 143 351
C=O 120 745
(both from a carboxylic acid)
NN 140 159
OO 148 494
ClCl 199 240
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As the number of bonds increases, bond length decreases and bond energy increases
i.e. the C C triple bond has three shared bonds, and thus has a shorter bond length and
higher bond energy than the C=C and CC bonds.
However multiple bonds also tend to be much more reactive! As will be discussed later, it
is very common to break multiple bonds of alkenes or alkynes, using a variety of reagents to
form other products with single bonds.
Geometric Isomers
geometric isomers isomers in which the attached groups differ from each other relative to
the double bond
cis- isomers attached groups are on the same side of the double bond
trans- isomers attached groups are on opposite sides of the double bond
examples:
C4H8 C4H8
cis-2-butene trans-2-butene
I. c. Alkynes
Hydrocarbons which contain at least one triple bond
Alkynes have the general formula CnH2n-2
examples:
C2H2 C3H4 C4H6
ethyne propyne 1-butyne
(acetylene)
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All alkynes end in -yne
When naming alkynes, find the longest chain containing a triple bond.
Carbon atoms of the longest chain are numbered from the end closest to the triple bond.
The position number of the triple bond is assigned to the first carbon atom of the triple
bond (i.e. the lowest possible number carbon).
ex 1: see 1-butyne above
ex 2:
2-hexyne
The simplest member of the alkyne family (C2H2, or HC CH ) is also known commonly
as acetylene.
Acetylene is a gas commonly used in acetylene torches it burns with a very hot flame,
and is often used to cut steel.
Alkyne nomenclature also sometimes uses acetylene as the parent group, naming
functional groups coming off the acetylene (though this is not correct IUPAC
nomenclature)
ex: CH3CH2C CCH3
ethylmethylacetylene
Rules for naming functional groups attached to alkynes are the same as the rules for alkenes:
The triple bond takes precedence! Number the carbons so that the triple bond occurs at
the lowest possible number carbon. Position numbers for functional groups thus depend
on the number assigned to the triple bond.
II. Functional Groups
functional group an atom or group of atoms that undergoes characteristic, predictable
reactions
chemical reactions usually occur at functional groups!!!
Characteristic IR
Functional Group Name Absorption (cm-1) Example
alkenyl 1680 1620
CH3CHCHCH3
2-butene
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alkynyl 2260 2100
CH3CCCH3
2-butyne
halogenoalkane
(organic halide) CH3CH2Br
bromoethane
alcohol 3550 3200 (hydroxyl) CH3CH2OH
ethanol
(ethyl alcohol)
ether 1050 1200
CH3CH2OCH2CH3
diethyl ether
aldehyde 1740 1690
CH3CHO
RCHO ethanal
ketone 1750 1680
CH3CH2COCH3
RCOR' 2-butanone
carboxylic acid 1780 1710
(carboxyl)
CH3CH2COOH
RCOOH propanoic acidester 1750 1735
CH3COOCH2CH3
RCOOR' ethyl ethanoate
amine 3500 3300
CH3CH2NH2
RNH2, RNHR' ethylamine
amide NH (3700 3500)
C=O (1690 1630)CH3CONH2
RCONH2, RCONHR' ethanamide
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Functional groups can exist as isomers, so be careful!
ex: propanal (CH3CH2CHO) vs. propanone (CH3COCH3)
ethanol (CH3CH2OH) vs. dimethyl ether (CH3OCH3)