1 / 20

cyclohexane

cyclohexane. cis -. 1,2-. dimethyl. cyclo. hexane. cis -1,2-dimethylcyclohexane. axial - equatorial. trans -. 1,2-dimethylcyclohexane. trans -1,2-dimethylcyclohexane. axial - axial. equatorial - equatorial. Optical isomerism. Stereocenter 4 different substituents. C * =. *. Br.

brie
Download Presentation

cyclohexane

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. cyclohexane cis- 1,2- dimethyl cyclo hexane cis-1,2-dimethylcyclohexane axial-equatorial trans- 1,2-dimethylcyclohexane trans-1,2-dimethylcyclohexane axial-axial equatorial-equatorial

  2. Optical isomerism Stereocenter 4 different substituents C*= *

  3. Br Br Fischer projections * C C * I Cl Cl I H H (+) (-) Br Br Enantiomers * * I Cl Cl I H H non-superimposable mirror images

  4. Enantiomers identical in most properties differ in: 1.interaction with polarized light 2. interaction with chiral environments Light interacts with molecules when it passes through them [interaction of electrical fields] When light encounters mirror image of molecule, interaction is reversed

  5. Polarized light (-) Oneenantiomer - rotate light to the left (+) Otherenantiomer - rotate light to the right in 50/50 mix - no net rotation racemic mixture one enantiomer - polarized light will be rotated optical activity

  6. Optical isomerism Stereocenter 4 different substituents C*= * * 3-methyl hexane bromo chloro iodo methane * * bromo cyclo pentane trans- 1,3-dibromo cyclopentane no C*

  7. Alkane Summary 1. Alkanes -sp3 hybridized 2. Relatively unreactive Substitution with halogens Combustion 3. Non-polar IMF = London Dispersion Forces size structure

  8. 4. Free rotation around C-C bonds conformations 5. Non-cyclic alkanes - structural isomers 6. Cyclic alkanes - geometric isomers cis-, trans- 7. Alkanes -optical isomers stereocenters C*

  9. alkyl halides 1o uv + Cl2 1o 3o 1o 2o .. .. :Cl:Cl: .. .. .. 2 :Cl. half-arrow = 1e- step 1 .. form mostly stability of free radicals 3o > 2o > 1o

  10. 3-methylhexane no reaction + OH- * stereocenter * + Br- + OH- C+ electrophile e- deficient + .. - : OH- nucleophile e- rich ..

  11. Nucleophilic Substitution SN1 * * + Br- + OH- reaction is 1st order in C7H15Br zero order in OH- reactants are optically active rate = k [R – X] products are optically inactive

  12. CH3 CH3 . . . . : : C2H5 – C – Br : C2H5 – C+ Br- . . . . C3H7 C3H7 Nucleophilic Substitution SN1 rate determining step unimolecular step 1 slow C+ carbocation (4 – ½ (6) – 0) = +1 reactants are optically active rate = k [R – X] products are optically inactive

  13. CH3 CH3 . . . . : : C2H5 – C – Br : C2H5 – C+ Br- . . . . C3H7 C3H7 . . CH3 . . : - O – H . . : H – O - . . C+ CH3 CH3 C3H7 HO C3H7 H7C3 OH C2H5 C2H5 C2H5 Nucleophilic Substitution SN1 step 1 slow step 2 * * reactants are optically active rate = k [R – X] products are optically inactive

  14. E C+ Nucleophilic Substitution SN1 Ea carbocation intermediate 1st order in R – X 2 products Nu – R + X- Nu- + R – X

  15. Nucleophilic Substitution SN2 * * + Br- + OH- reaction is 1st order in C4H9Br 1st order in OH- rate = k [R – X] [OH-] reactants are optically active products are optically active

  16. H H H . . . . : C – Br HO – C – CH3 H-O . . : ---C---Br . . CH3 C2H5 C2H5 CH3 C2H5 . . : H – O - . . C2H5 C2H5 . . :Br:- . . H Br HO H CH3 CH3 Nucleophilic Substitution SN2 rate determining step bimolecular step 1 * slow transition state stereocenter inverted reactants are optically active rate = k [R – X][OH-] products are optically active

  17.  -  - Nu---C---X E Nucleophilic Substitution SN2 Ea 1st order in R – X 1st order in Nu- 1 product Nu – R + X- Nu- + R – X

  18. SN1 or SN2 H R R R H R 3o R –X SN1 carbocation 3o > 2o > 1o yes 2o R –X ? 1o R –X no

  19. SN1 or SN2 1o R – X yes SN2 transition state 2o R –X ? 3o R – X no

  20. SN1 or SN2 3o R –X SN2 1o R – X yes yes SN1 2o R –X 2o R –X ? ? 1o R –X no 3o R – X no Other factors influencing rates: Nucleophile : SH- I- CN- charged OH- neutral NH3 H2O Solvent Temperature

More Related