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Chapter 8 Alkenes and alkynes I.Properties and synthesis8.1
IntroductionAlkenes are hydrocarbons whose molecules contain the
carbon-carbon double bond.
Hydrocarbons whose molecules contain the carbon-carbon triple
bond are called alkynes.
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8.2 Nomenclature of alkenes and cycloalkenes
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The IUPAC rules for naming alkenes are similar in many respects
to those for naming alkanesSelecting the longest chain that
contains the double bondNumber the chain
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3. Indicate the locations of the substituent groups
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4. Number substituted cycloalkenes in the way that gives the
carbon atoms of the double bond the 1- and 2- positions and that
also gives the substituent groups the lower numbers at the first
point of difference
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5. Two frequently encountered alkenyl groups are the vinyl group
and the allyl group.
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6. Designate the geometry of a double bond of a disubstituted
alkene with the prefixes cis- and trans-
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8.2A The ( E )-( Z ) System for designation alkene
diastereomers
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8.3 Nomenclature of alkynes8.3A IUPAC Nomenclature
Unbranched alkynes, for example, are named by replacing the ane
of the name of the corresponding alkane with the ending yne. The
chain is numbered in order to give the carbon atoms of the triple
bond the lower possible numbers.
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8.4 Physical properties of alkenes and alkynes8.5 Hydrogenation
of alkenes
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8.6 Hydrogenation: The function of the catalyst
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Catalytic hydrogen and Syn--addition
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8.6A Syn and anti additions
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8.7A Syn addition of hydrogen: Synthesis of cis-alkenes
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8.7B Anti addition of hydrogen: Synthesis of trans-alkenes
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8.9 Relative stabilities of alkenes8.9A Heats of
hydrogenation
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The order of stabilities;
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8.9B Relative stabilities from heats of combustion
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8.9C Overall relative stabilities of alkenes
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8.10 CycloalkenesThe rings of cycloalkenes containing five
carbon atoms or fewer exist only in the cis form. Therefore, fewer
exist in the trans form because of the ring strain.
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Cis- and trans-Cycloalkenes
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8.11 Synthesis of alkenes via elimination reactions
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8.12 Dehydrohalogenation of alkyl halides
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8.12A E2 reactions: The orientation of the double bond in the
product. Zaltsevs Rule(----
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8.12C The stereochemistry of E2 reactions:
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8.13 Dehydration of alcoholsThe experimental
conditions----temperature and acid concentration
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Ease of Dehydration
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8.13A Mechanism of alcohol dehydration: An E1 reaction
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Ease of dehydration for E1 reaction
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8.15 Carbocation stability and the occurrence of molecular
rearrangements (
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The type of rearrengement
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Rearrengement mechanism (E1 reaction)
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8.16 Alkenes by debromination of vicinal dibromides
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8.17 Summary of methods for the preparation of alkenes
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2. Dehydration of alcohols
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3. Dehalogenation of vic-dibromides
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4. Hydrogenlation of alkynes
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8.18 Synthesis of alkynes by elimination reaction
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8.19 The Acidity of terminal alkynesThe hydrogen atoms of ethyne
are considerably more acidic than those of ethene or ethane
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Relative acidity;
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Relative AcidityConjugate acid)(Conjugate base)
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8.20 Replacement of the acetylenic hydrogen atom of terminal
alkynesSodium ethynide and other sodium alkynides can be prepared
by treating terminal alkynes with sodium amide (NaNH2) in liquid
ammonia
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It applied synthesis (SN2)
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8.21 Other metal acetylidesEthyne and terminal alkynes also form
metal derivatives with silver and copper (I) ions
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As a method for separating terminal alkynes from alkynes that
have an internal triple bond
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Homework; 8.22, 8.24, 8.25, 8.29, 8.30Happy New Year!
Good luck for you final organic chemistry test!