Chem357_Alkyne_Chem__FINAL_Student_

Chem357_Alkyne_Chem__FINAL_Student_ - 1 Reactions of...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon

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

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

Unformatted text preview: 1 Reactions of Alkynes Reactions of Alkynes Paula Y. Paula Y. Bruice Bruice , , Chapter 6 Chapter 6 2 Some chemistry of Alkynes is similar to that explored already for Alkenes but there are distinct differences. Reactions of Alkynes Reactions of Alkynes e.g. H 2 Pt o r Pd/C H H H 2 (2 equiv.) Pt o r Pd/C H H H H Br 2 Br Br Br 2 Br Br Br Br (2 equiv.) HYDROGENATION HALOGENATION 3 Reactions of Alkynes Reactions of Alkynes But compare the following. C C H C OH C H H H C C H C O C H H H a ketone an alcohol H H H 2 O H H 2 O 4 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation H 2 (2 equiv.) Pd/C H H H H H H excess H 2 H 2 H 2 (1 equiv.) Pd/C H H H H What happens when ONLY one equivalent of H 2 is used? Pd/C Pd/C + unreacted alkyne H H + ONLY small amount Why? H H Recall the surface delivery of hydrogen to just one face giving SYN ADDITION M I X T U R E 3 Reactions of Alkynes Reactions of Alkynes But compare the following. C C H C OH C H H H C C H C O C H H H a ketone an alcohol H H H 2 O H H 2 O 4 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation H 2 (2 equiv.) Pd/C H H H H H H excess H 2 H 2 H 2 (1 equiv.) Pd/C H H H H What happens when ONLY one equivalent of H 2 is used? Pd/C Pd/C + unreacted alkyne H H + ONLY small amount Why? H H Recall the surface delivery of hydrogen to just one face giving SYN ADDITION M I X T U R E 5 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation H 2 Pd/C H H H H H H H 2 Pd/C Alkenes are significantly more reactive in addition reactions than Alkynes. SLOW FAST The alkene reacts as soon as it is formed. Here, the H 2 would be a limiting reagent. s p h y b r i d i z e d c a r b o n s h o l d t h e i r e l e c t r o n s m o r e t i g h t l y t h a n a n s p 2 c a r b o n 6 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation Consider the following: H H 2 (1 equiv.) Pd/C H 2 (1 equiv.) Pd/C ? ? What is the MAJOR product? 7 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation CH 3 CH 2 CH 3 CH 3 CH 3 CH 2 H H Consider the utility in the following reactions... H CH 3 CH 2 H CH 3 cis-alkene trans-alkene ? ? Br 2 Br 2 CH 3 H Br Br H (+ enantiomer) (2 S ,3 R )-2,3-dibromopentane H H Br Br CH 3 (+ enantiomer) (2 R ,3 R )-2,3-dibromopentane 8 Reactions of Alkynes - Hydrogenation Reactions of Alkynes - Hydrogenation CH 3 CH 2 CH 3 CH 3 CH 3 CH 2 H H cis-alkene Lindlar's Catalyst H 2 Lindlar's catalyst is a "POISONED" or "DEACTIVATED" hydrogenation catalyst....
View Full Document

This note was uploaded on 03/29/2009 for the course CHEM 3570 taught by Professor Ganem, b during the Fall '06 term at Cornell University (Engineering School).

Page1 / 18

Chem357_Alkyne_Chem__FINAL_Student_ - 1 Reactions of...

This preview shows document pages 1 - 5. Sign up to view the full document.

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