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Organic Chemistry

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Title: Organic Chemistry


1
Organic Chemistry
William H. Brown Christopher S. Foote
2
Alkenes I
  • Chapter 5

3
Unsaturated Hydrocarbons
  • Unsaturated hydrocarbon contains one or more
    carbon-carbon double or triple bonds
  • Alkene contains a carbon-carbon double bond and
    has the general formula CnH2n
  • Alkyne contains a carbon-carbon triple bond and
    has the general formula CnH2n-2

4
Unsaturated Hydrocarbons
  • Arenes benzene and its derivatives (Ch 20-21)

5
Benzene Phenyl Group
  • We do not study benzene and its derivatives until
    Chapters 20 21
  • but, we show structural formulas of compounds
    containing the phenyl group before that time
  • the phenyl group is not reactive under any of
    the conditions we describe in Ch 6-19

6
Structure of Alkenes
  • The two carbon atoms of a double bond and the
    four atoms attached to them lie in a plane, with
    bond angles of approximately 120
  • A double bond consists of
  • one sigma bond formed by overlap of sp2 hybrid
    orbitals
  • one pi bond formed by overlap of parallel 2p
    orbitals
  • it takes approx. 264 kJ (63 kcal)/mol to break
    the pi bond in ethylene

7
Restricted rotation about CC
8
Cis,Trans Isomerism
  • Cis,trans isomers isomers that have the same
    connectivity but a different arrangement of their
    atoms in space due to the presence of a ring or a
    carbon-carbon double bond

9
IUPAC Nomenclature
  • 1. Number the longest chain of carbon atoms that
    contains the double bond in the direction that
    gives the carbons of the double bond the lowest
    numbers
  • 2. Locate the double bond by the number of its
    first carbon
  • 3. Name substituents
  • 4. Number the carbon, locate and name
    substituents, locate the double bond, and name
    the main chain.

10
Alkenyl Groups
11
Common Names
  • Despite the precision and universal acceptance of
    IUPAC nomenclature, some alkenes, particularly
    low-molecular-weight ones, are known almost
    exclusively by their common names

12
Configuration
  • The cis,trans system configuration is determined
    by the orientation of atoms of the main chain

13
Configuration - E,Z
  • uses priority rules (Chapter 3)
  • if groups of higher priority are on the same
    side, configuration is Z (German, zusammen)
  • if groups of higher priority are on opposite
    sides, configuration is E (German, entgegen)

14
Configuration - E,Z
  • Example name each alkene and specify its
    configuration by the E,Z system

15
Cis,Trans Isomerism
  • Cycloalkenes
  • configuration of the double bond in cyclopropene
    through cycloheptene must be cis
  • cyclopentene is only slightly puckered

16
Cis,Trans Isomerism
  • the configuration of the double bond in
    cyclohexene must be cis
  • cyclohexene is puckered

17
Cis,Trans Isomerism
  • Cycloalkenes
  • trans-cyclooctene is the smallest
    trans-cycloalkene stable at 25C
  • the cis isomer is 38 kJ (9.1 kcal)/mol more
    stable than the trans isomer.

18
Physical Properties
  • Alkenes are nonpolar compounds
  • The only attractive forces between their
    molecules are dispersion forces
  • The physical properties of alkenes are similar to
    those of alkanes

19
Terpenes
  • Terpene a compound whose carbon skeleton can be
    divided into two or more units identical with the
    carbon skeleton of isoprene

20
Terpenes
  • Myrcene, C10H16, a component of bayberry wax and
    oils of bay and verbena
  • Menthol, from peppermint

21
Terpenes
  • ?-Pinene, from turpentine
  • camphor, from the camphor tree

22
Terpenes
  • Vitamin A (retinol)
  • how many stereoisomers are possible for this
    terpene alcohol?

23
Prob 5.7
  • Using the VSEPR model, predict all bond
    angles about each circled atom.

24
Prob 5.12
  • Name these alkenes and cycloalkenes.

25
Prob 5.13
  • Arrange the groups in each set in order of
    increasing priority.

26
Prob 5.14
  • Assign an E or Z configuration to each
    compound. Also assign a cis or trans
    configuration to each.

27
Prob 5.16
  • For each molecule that shows cis,trans
    isomerism, draw the cis isomer.

28
Prob 5.17
  • Draw structural formulas for all compounds of
    molecular formula C5H10 that are
  • (a) alkenes that do not show cis,trans isomerism.
  • (b) alkenes that do show cis,trans isomerism.
  • (c) cycloalkanes that do not show cis,trans
    isomerism.
  • (d) cycloalkanes that do show cis,trans isomerism.

29
Prob 5.19
  • Draw a structural formula of a bromoalkene of
    molecular formula C5H9Br that shows
  • (a) neither E,Z isomerism nor chirality.
  • (b) E,Z isomerism but not chirality.
  • (c) chirality but not E,Z isomerism.
  • (d) both chirality and E,Z isomerism.

30
Prob 5.23
  • Which alkenes exist as pairs of cis,trans
    isomers? For each that does, draw the trans
    isomer.

31
Prob 5.24
  • Show that four stereoisomers are possible for
    this compound. Draw the stereoisomer with an E
    configuration at the double bond and an R
    configuration at the stereocenter.

32
Prob 5.28
  • Show that warburganal is a terpene. Label all
    stereocenters and state how many stereoisomers
    are possible for a molecule of this structure.

33
Prob 5.29
  • Show that santonin is a terpene. Label all
    stereocenters and tell how many stereoisomers are
    possible for the molecule of this structure.

34
Prob 5.30
  • (a) Show that zoapatanol is a terpene.
  • (b)Specify the configuration at the double
    bond to the seven-membered ring.
  • (c) How many stereoisomers are possible for
    this molecule?

35
Prob 5.31 Pyrethrin II
  • Label all stereocenters in pyrethrin II. How
    many stereoisomers are possible for this molecule?

36
Prob 5.31 Pyrethrosin
  • Show that pyrethrosin is a terpene. Label all
    stereocenters in pyrethrosin and state how many
    stereoisomers are possible for it.

37
Alkenes I
  • End Chapter 5
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