123.202 Lecture 11 - alkynes

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©[email protected]flickr dienes & alkynes ..LECTURE ELEVEN
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123.202 lecture 11 alkynes and dienes

Transcript of 123.202 Lecture 11 - alkynes

2. PREVIOUSLY... Brradicals... 3. 12 dienes HHCHHisolated conjugated cumulated dienediene dieneallene 4. cumulated dienes allenes mirrorHH Ph Ph C C HH PhPh 5. (2py+2py) Ph H C C CHPhorbitalsH Ph C H Ph 6. (2py+2py)sp Ph H sp2C CCHPh(2pz+2pz) shape90 HPhCH Ph 7. conjugated dienesstabilisation 8. resonance stabilisation 9. resonance stabilisation Observed ExpectedkJmol1kJmol1 127 253 254 254 254 239 254 10. 13 electrophilic addition to conjugated dienes HXXX H H HX XH H X regioisomers 11. how many? regioisomers ?X XH H HHHXXXX H 12. how many regioisomers ?X XH H HHHXXXX H 13. how many regioisomers ?X XH H HHHXXXX leastH favoured 14. 13 electrophilic addition to conjugated dienes Br2Br 2 x Br2 Br BrBr 15. 13 electrophilic addition to conjugated dienes Br2BrBr Br2 BrBr regioisomers 16. mechanism Br Br Br BrBrBrBr BrBr 17. alkynes [email protected] 18. 14 acidity of alkynes R HNaNH2 very strong base R NaNHH2 19. X not acidic H HH RH R H 20. Horia [email protected] 21. sp sp2sp3 (50% s) (33% s)(25% s) molecularorbitals 22. decreasing acid strengthOH H O H H H N HCl >>> O > O > >HH > R OHH H R R R O O NO O Cl