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Bonding, Nomenclature, Properties

Z. E. chapter 5. Alkenes. Bonding, Nomenclature, Properties. Structure Hydrogen Deficiency Nomenclature Physical Properties Naturally Occurring Alkenes/Terpenes. b. R or S?. R or S?. Which is 2S , 3R -propoxyphen & 2R , 3S -propoxyphen?. ( 2R , 3S )-.

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Bonding, Nomenclature, Properties

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  1. Z E chapter 5 Alkenes Bonding, Nomenclature, Properties Structure Hydrogen Deficiency Nomenclature Physical Properties Naturally Occurring Alkenes/Terpenes b

  2. R or S? R or S?

  3. Which is 2S,3R-propoxyphen & 2R,3S-propoxyphen? (2R,3S)- antitussive NovraD | DarvoN analgesic

  4. 1. Alkene: contains a carbon-carbon doublebond ethene 2.Alkyne: contains a carbon-carbon triple bond(Ch 7) ethyne(acetylene) 3.Arene: benzene and its derivatives (Ch 21-22) phenyl. Ph UnsaturatedHydrocarbons

  5. Double Bond: 1-bond formed by overlap of 2 sp2 hybrid orbitals 1 -bondformed by overlap of 2 parallel 2p orbitals -bond -bonded atoms all in a plane  trigonal - bond angles ~ 120° H C H perpendicular H C H to the plane Structure of Alkenes

  6. No rotation about a C=C bond - why? H C H H C H Structure of Alkenes Rotation requires breaking  bond ~63 kcal/mol

  7. Number chain - olefin lowest number #- indicates C=C in chain 6 5 1 2 4 3 Nomenclature IUPAC: Root name - longest continuous chain containing the olefin. alkene Number of C’s in C=C chain 2-ethyl-4-methyl-1-pentene 2-hexene

  8. IUPAC names? 7-bromo-4-(2-iodoethyl)-6-methyl-3-octene (7S)-7-bromo-4-(2-iodoethyl)-6-methyl-3-octene

  9. Number chain - olefin lowest number #-cycloalkene #- #- alkene Nomenclature IUPAC: Root name - longest continuous chain containing the olefin alkene indicates C=C in chain Number of C’s in chain with an C=C Cyclic Olefin (functional group) - positions 1,2 Number around the ring to best accommodate substituents

  10. IUPAC names? cycloheptene -bromo- -methyl 4-bromo-4-methylcycloheptene (3 ,5 )- -chloro- -fluoro- -methylcyclopent-1-ene (3S,5R)-5-chloro-1-fluoro-3-methylcyclopent-1-ene

  11. Cl Cl Cl H C C C C H H H Cl The Cis,Trans Systemrecall cis/trans isomers cis-1,2-dichloroethene trans-1,2-dichloroethene transgenerally more stable thancis - dipoles and 1,2 interactions

  12. Configuration is determined by the orientation of atoms of the main chain The Cis,Trans System trans-3-hexene cis-3,4-dimethyl-2-pentene

  13. C8 limited stability as trans Cycloalkenes- 3 to 7 “cis” olefins rings not large enough to accommodate trans double bonds

  14. uses priority rules (Chapter 3) higher priority groups - same side, Z higher priority - opposite sides, E E,Z Configuration E Z

  15. H C C H C C H H C C C C C C H C C H C C H H E/Z - priorities of groups on ends of C=C (1) Atom assigned a priority, higher atomic number higher priority. (2) Isotopes - higher atomic mass, higher priority 1H < 2H < 3H [H < D < T] (3) If priority the same, go to the next set of atoms: -CH2-H < -CH2-O-H < -CH2-Cl (4) double (triple) bonds replaced by single bonds.

  16. Example:name each alkene and specify its configuration by the E,Z system The E,Z System

  17. Stereochemistry? IUPAC names? ?(trans)-longest chain? (3Z,7S)-7-bromo-4-(2-chloroethyl)-6-methyl-3-octene (7S)-7-bromo-4-(2-chloroethyl)-6-methyl-3-octene (S)-6-ethyl-1-fluoro-5,5-dimethylcyclooctene

  18. If same atoms, priority goes to the next point of difference 9-bromo-5-(2-methylpropyl)-4-nonene (E)- (4E)-

  19. 1 2 7 3 4 6 5 Nomenclature - more than 1 unsaturated group Diene (or diyne, en-yne) longest chain (ring) with both groups: #,#-alkadiene #,#-alkadiyne #-alken-#-yne (if the same ene > yne). number so enes (enyne, ynes) have the lowest possible number 1,4-cycloheptadiene

  20. alkenes with n double bonds (that can be cis, trans)2n stereoisomers are possible example 2,4-heptadiene Dienes, Trienes, and Polyenes

  21. Dienes - E or Z per olefin with number 1,6-dichloro-2,4-dimethyl-2,6-decadiene ( 2Z, 4S, 6E)- ( 2Z, 4S, 6E)- to 6.1

  22. Alkenes are nonpolar compounds attractive forces between molecules are dispersion forces The physical properties of alkenes are similar to those of alkanes Physical Properties to 6.1

  23. Common Names used lab & lecture not on tests to 6.1

  24. Index of hydrogen deficiency (IHD): IHD =  (number of rings + number ofbonds) Compare HsofalkanewithHsin a compound CnH2n+2CnHx (14 - 10) 2 = ) (H - H reference molecule IHD = 2 Index of Hydrogen Deficiency e.g. C6H10 C6H2(6)+2 = 2 to 6.1

  25. Other elements present F, Cl, Br, I add one H - (Group 7) O No correction to unknown formula N, P subtract one H (Group 5) C6H8ClNO C6H9Cl C6H7ClO e.g. 8 + 1 - 1 7 + 1 9 + 1 Index of Hydrogen Deficiency to 6.1

  26. Problem: calculate the IHD for niacin, molecular formula C6H6N2O reference hydrocarbon C6H14 IHD = [14 - (6-2)]/2 = 5 Index of Hydrogen Deficiency end to 6.1

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