ALKENES are hydrocarbons:

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ALKENES are hydrocarbons with CC bonds of
general formula CnH2n having 120 bond angles
and trigonal planar shape around the C
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Examples
H H CC H H
ethylene
H CH3 CC H H
propene
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A CC is made up of 2 types of bonds The s bond
is a standard C-C. The p bond is weaker than
s. Overall, the CC is stronger (but not 2x
stronger) and shorter than a C-C.
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Naming alkenes 1. Find longest chain of C that
contains the CC. 2. Number chain to give one
of the C in CC the lowest possible locant. 3.
Change name of parent alkane to alkene.
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4. Give the lower locant number for a CC in
front of the parent alkene name. 5. Number and
name other substituents as usual.
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Naming cycloalkenes 1. Start numbering of ring C
at one of the C in CC. 2. Position 2 is the
second C of the CC. 3. Count in the direction
which gives other substituents the lower set
of locant .
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Stereoisomers are isomers ( same formula),
having same constitution ( same kinds sequence
of bonds), but permanently different
arrangements of groups in space.
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Stereoisomers are of several types, depending on
what phenomenon causes them to exist. Geometric
isomers are stereoisomers because of restricted
rotation around bonds (C-C or CC).
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In alkenes the two bonds between the C of the CC
prevents free rotation of the groups around the
CC bond. cis and trans geometric isomers have
different physical and chemical properties they
are distinctly different compounds.
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Compare the corresponding alkenes H
H CH3 H CC CC
CH3 CH3 H CH3
cis-2-butene trans-2-butene
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When can an alkene exist as geometric
isomers? gt the same C of CC must have two
different groups bonded to it. CH3CH2 H
CC 1-butene no H
H cis or trans
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H
CH3
CC
CH3
CH2CH3
2-methyl-2-pentene has no geometric isomer
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Addition Reactions are typical of
alkenes. General schematic equation CC
X-Y ----gt C-C
X Y
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In an addition reaction the p bond of CC
breaks the covalent bond between X,Y
breaks new C-X and C-Y s bonds form
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When bonds break and form in reactions, the
shared electron pairs are scrambled or rearranged
... to be shared by different atoms.
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In the addition reaction, X and Y can be the
same element or different elements. Examples of
XY H2, Cl2, Br2 Example of X, Y Different H2O
written as H-OH
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CH3-CHCH2 H2, Pt (metal
catalyst)
CH3CH-CH2 CH3CH2CH3 H H
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so, the general equation is alkene H2 --gt
alkane
This process is called catalytic reduction or
hydrogenation because the H2 is added with the
help of a catalyst.
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HOH (water) alone does not react with an alkene
it requires a catalyst. Addition of water to the
alkene CC is called hydration . In lab the
catalyst is H (acid), often from H2SO4. In a
living cell the catalyst is an enzyme.
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Markovnikov found when H-X adds to a CC of
alkene, H attaches to the C of CC that already
had more H bonded to it. H-X H-Cl, H-Br, H-I,
H-OH
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Example CH3CH2CHCH2 H2O ----gt
CH3CH2CH-CH2 OH H more
commonly written as CH3CH2CH-CH3 OH
H
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Alkynes are hydrocarbons that contain a C
C have general formula CnH2n-2 have linear
geometry, 180 bond angle
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Naming Alkynes 1. find longest chain that
includes C C. 2. change parent name of
longest chain from alkane to alkyne. 3.
give lowest possible locant to the first C of
C C. 4. locate other substituents as usual.
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Aromatic Compounds usually contain six
double-bonded carbon atoms in a ring have
alternating C-C CC have a flat ring
structure do NOT undergo addition reactions
like alkenes.
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Some important aromatic compounds
CH3
NH2
OH
benzene aniline
toluene phenol
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When a benzene ring is a substituent on a parent
chain, it is called phenyl
CH3CHCCH2CH2CH2CH2CH3
3-phenyl-2-octene