L14a - Stereochemistry of alkene hydrogenation Section 6.3...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 1 Section 6.3 © Kay Sandberg Stereochemistry of alkene hydrogenation + D 2 Pt © Kay Sandberg D 2 Ni H D = deuterium = 2 H 1p + e - 1n o ,1p + e - H = 1 H 1 proton in nucleus 1 proton & 1 neutron in nucleus In reactions D reacts the same as H H 3 C H D D another hydrogen isotope D D D D and most abundant hydrogen isotope H 3 C H D D D H 3 C D H DC H 3 DH mirror images 3 ©Dr. Kay Sandberg Last lecture This lecture Alkene reactions More alkene reactions 2) electrophilic addition of HX 3) free radical addition of HBr 1) Reviewed dehydration of alcohol Alkene preparations 2) Examined dehydrohalogenation of alkyl halide 1) hydrogenation 4 Section 6.3 © Kay Sandberg Both atoms/groups add to the same face of the alkene X Y Stereochemistry of alkene hydrogenation Syn addition Atoms/groups add to opposite faces of the alkene Anti addition X-Y X-Y Y X 5 Section 6.3 © Kay Sandberg Stereochemistry of alkene hydrogenation Even though hydrogenation is stereospecific… + H 2 H H JME Only use wedge/dashed tool for alkane product if alkene starting material is cycloalkene & tetrasubstituted or when using D 2 Pt H H D 2 you will need to use wedge or dashed bonds on the ring. H 6 H 3 C CH 3 H 3 C H H 2 Ni H 3 C CH 3 H 3 C H H H α -pinene H 3 C CH 3 H H H CH 3 + Section 6.3 © Kay Sandberg Stereochemistry of alkene hydrogenation Only product Effectively blocks top face - steric effect AB Both exhibit syn addition
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 7 © Kay Sandberg Reactions of alkenes: Addition of HX Section 6.4 H X + H - X alkene hydrogen halide alkyl halide π e - s δ - δ - δ + Uphill or downhill? uphil downhil 9% 91 % 1. uphill 2. downhill H X + © Kay Sandberg Reactions of alkenes: Addition of HX Section 6.4 H X + H X + H X alkene weak base ( π electrons) δ - δ + δ - HX strong acid (HCl, HBr, HI) slow weak base strong acid strong conjugate acid weak conjugate base Step 1 H X + © Kay Sandberg Reactions of alkenes: Addition of HX Section 6.4 H X + H X + H X alkene weak base ( π electrons) δ - δ + δ - HX strong acid (HCl, HBr, HI) slow weak base strong acid strong conjugate acid weak conjugate base Potential E rxn progression Step 1 10 H X + © Kay Sandberg + H X H X Electrophilic addition δ - δ + δ - slow fast Reactions of alkenes: Addition of HX Section 6.4 H X + H X step 1 step 2 rxn progression 11 © Kay Sandberg Reactions of alkenes: Addition of HX Section 6.4 H X + H X Good: started out π , ended up σ no longer bonded to H electron perspective halogen perspective halide ions: “stink” as Bronsted bases , but they are good nucleophiles Bad : entropy perspective – SM: 2 species; P: 1 species Does anything “ good ” result? (i.e. lower energy) Does anything “ bad ” result? (i.e. higher energy) Δ H o = -54 kJ/mol Δ G o = Δ H o - T Δ S o 12 © Kay Sandberg Reactions of alkenes: Addition of HX Section 6.4 Br CH 3 CH 2 C H 2 CHCH 2 CH 3 3- bromo hexane H 3 CH 2 C H H CH 2 CH 3 + H Br cis -3-hexene -30 o CHCl 3 H I >H Br Cl >> H F Reactivity of HX Most acidic, most reactive Least acidic, least reactive Br
Background image of page 2
3 13 © Kay Sandberg this not this X H R CH CH 2 H X R CH CH 2 R H H H + H X Reactions of alkenes: Addition of HX Section 6.5
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/30/2009 for the course CH ORGANIC CH taught by Professor Kaysandberg during the Spring '09 term at N.C. State.

Page1 / 9

L14a - Stereochemistry of alkene hydrogenation Section 6.3...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online