100 STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTION: is a double bond between C-2 and C-3. The rest of the name provides the information that there are four methyl groups and that they are located at C-2, C-6, C-10, and c-14 2, 6, 10, 14-Tetramethyl-2-pen allyl group is CH CHCH. Allylisothiocyanate is therefore CH2CHCH,N-C-S 5.25(a) The E configuration means that the higher priority groups are on opposite sides of the double CH, CH, CH, CH, CH,OH Higher (E)-6-Nonen-1-ol (b) Geraniol has two double bonds, but only one of them, the one between C-2 and C-3, is capa ble of stereochemical variation. Of the groups at C-2, CH,OH is of higher priority than H. At C-3, CH, CH, outranks CH3. Higher priority groups are on opposite sides of the double bond in the E isomer; hence geraniol has the structure shown (CH3)C=CHCH, CH, H3C CHOH (c) Since nerol is a stereoisomer of geraniol, it has the same constitution and differs from gera- niol only in having the Z configuration of the double bond (CH),C=CHCH, CH CHOH (d) Beginning at the C-6, C-7 double bond, we see that the propyl group is of higher priority than the methyl group at C-7. Since the C-6, C-7 double bond is E, the propyl group must be on the opposite side of the higher priority group at C-6, where the Ch, fragment has a higher prior ity than hydrogen. We therefore write for the stereochemistry of the C-6, C-7 double bond as Higher CH3 CH, CH2 H Lower Lower CH,- Higher At C-2, CH,OH is of higher priority than H; and at C-3, CH,CH,C-is of higher priority than CH, CH3. The double-bond configuration at C-2 is Z. Therefore H CCH.CH CHOH Higher Lower CH, Lower Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
is a double bond between C-2 and C-3. The rest of the name provides the information that there are four methyl groups and that they are located at C-2, C-6, C-10, and C-14. (b) An allyl group is CH2?CHCH2@ . Allyl isothiocyanate is therefore CH2?CHCH2N?C?S. 5.25 (a) The E configuration means that the higher priority groups are on opposite sides of the double bond. (b) Geraniol has two double bonds, but only one of them, the one between C-2 and C-3, is capable of stereochemical variation. Of the groups at C-2, CH2OH is of higher priority than H. At C-3, CH2CH2 outranks CH3. Higher priority groups are on opposite sides of the double bond in the E isomer; hence geraniol has the structure shown. (c) Since nerol is a stereoisomer of geraniol, it has the same constitution and differs from geraniol only in having the Z configuration of the double bond. (d) Beginning at the C-6, C-7 double bond, we see that the propyl group is of higher priority than the methyl group at C-7. Since the C-6, C-7 double bond is E, the propyl group must be on the opposite side of the higher priority group at C-6, where the CH2 fragment has a higher priority than hydrogen. We therefore write for the stereochemistry of the C-6, C-7 double bond as: At C-2, CH2OH is of higher priority than H; and at C-3, CH2CH2C@ is of higher priority than CH2CH3. The double-bond configuration at C-2 is Z. Therefore C C CH3CH2 CCH2CH2 H Higher CH2OH Lower Higher Lower 3 2 6 5 4 1 E C C H3C CH3CH2CH2 H CH2 Higher Lower Higher Lower 7 6 10 9 8 5 C C H3C CHCH2CH2 (CH3)2C H CH2OH Nerol C C H3C CHCH2CH2 (CH3)2C H CH2OH Geraniol C C H CH3CH2 H CH2CH2CH2CH2CH2OH Higher Lower Higher Lower (E)-6-Nonen-1-ol 2,6,10,14-Tetramethyl-2-pentadecene 100 STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS 101 Combining the two partial structures, we obtain full structure of the codling moths sex pheromone CH, CH,CH H,C CH,CH, CHOH CH3CH2 H The compound is(2Z, 6E)-3-ethyl-7-methyl-2, 6-decadien-1-ol (e) The sex pheromone of the honeybee is(E)-9-oxo-2-decenoic acid, with the structure Higher CH3C(CH2)4CH Lower Lower COH Higher (f)Looking first at the C-2, C-3 double bond of the cecropia moths growth hormone CH-CH, CH, CH2 CH3 CO,CH we find that its configuration is E, since the higher priority groups are on opposite sides of the HC、 COCH -CH,CH, The configuration of the C-6C-7 double bond is also e. CH3CH CH,CH,- High CH,CH Lower 5.26 We havent covered, and wont cover, how to calculate the size of a dipole moment, but we can de cide whether a compound has a dipole moment or not Only compound B has dipole moment. The individual bond dipoles in A, C, and d cancel; therefore, none of these three has a dipole moment. HC、×CH CH H C 5.27 The alkenes are listed as follows in order of decreasing heat of combustion: 2,4,4-Trimethyl-2-pentene: 5293 kJ/mol (1264.9 kcal/mol). Highe heat of combustion because it is C&H16; all others are CH 1-Heptene: 4658 kJ/mol (1113. 4 kcal/mol). Monosubstituted double bond; therefore least stable C7H14 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
Combining the two partial structures, we obtain for the full structure of the codling moth’s sex pheromone The compound is (2Z,6E)-3-ethyl-7-methyl-2,6-decadien-1-ol. (e) The sex pheromone of the honeybee is (E)-9-oxo-2-decenoic acid, with the structure ( f ) Looking first at the C-2, C-3 double bond of the cecropia moth’s growth hormone we find that its configuration is E, since the higher priority groups are on opposite sides of the double bond. The configuration of the C-6, C-7 double bond is also E. 5.26 We haven’t covered, and won’t cover, how to calculate the size of a dipole moment, but we can decide whether a compound has a dipole moment or not. Only compound B has dipole moment. The individual bond dipoles in A, C, and D cancel; therefore, none of these three has a dipole moment. 5.27 The alkenes are listed as follows in order of decreasing heat of combustion: (e) 2,4,4-Trimethyl-2-pentene; 5293 kJ/mol (1264.9 kcal/mol). Highest heat of combustion because it is C8H16; all others are C7H14. (a) 1-Heptene; 4658 kJ/mol (1113.4 kcal/mol). Monosubstituted double bond; therefore least stable C7H14 isomer. H3C H3C CH3 CH3 C C A ( 0 D) Cl H3C CH3 Cl C C C ( 0 D) Cl Cl Cl Cl C C D ( 0 D) H3C Cl CH3 Cl C C B (has a dipole moment) C C C CH2CH2 CH3CH2 H CH2CH2 Higher Lower Higher Lower 7 6 10 9 8 5 4 C C CH2CH2 H3C H CO2CH3 Higher Lower Higher Lower 3 2 5 4 1 H3C CH3CH2 CH3CH2 CO2CH3 CH3 H H O 6 3 2 7 C C H CH3C(CH2)4CH2 H CO2H Higher Lower Higher Lower O C C CH3CH2 CH2CH2 H CH2OH C C H3C CH3CH2CH2 H STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS 101 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website