CHEM 2211 1nd Edition Lecture 24Outline of Last Lecture I. Nomenclature of alkynes II. Reaction of alkynes Outline of Current Lecture I. Reactions of alkynes cont. Current LectureReactions of alkynes continued The addition of boron to alkynes: hydroboration- oxidation - BH3 or R2BH (in THF) is added to the alkyne - After the addition a second step takes place o Aqueous sodium hydroxide and hydrogen peroxide are added - The final product of this reaction will be an enol o But an enol will readily rearrange into a ketone Reaction and mechanism: H3C CH3H3C CH3CH3C = CCH3 + R2BH THF C = C HO-, H2O2/ H2O C = C H B-R H OHR Enol Mechanism for Enol to Ketone H3C CH3OC =C CH3CH2CCH3These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.H OH - A base removes a proton from the enol - A pie bond forms between oxygen and carbon, as the pie bond between the two carbons breaks, carbon picks up a proton from water o Breaking the statement above down HO- comes in an takes the H off of OH in the enol This kicks the bonding electrons onto O - Forming the before said pie bond The H that was taken by HO- is then kicked back onto the C in the double bond making it a single bond The addition of Hydrogen to an Alkyne - The addition of H to alkynes is called hydrogenation - the reaction takes place in H2 over Pd/C o this takes an alkyne all the way to an alkane - it can be stop in alkene stage if poisoned with a metal catalyst o most common is the lindlar catalyst Reaction all the way to an alkane CH3CH2C = CH H2/ Pd/C CH3CH2CH = CH2 H2/ Pd/C CH3CH2CH2CH3Alkyne Alkene Alkane The highlighted area is where the H is attaching to break the triple bond into a double and then into a single Reaction when stopped with a metal catalyst CH3CH2C = CH + H2 Lindlar/ catalyst CH3CH2CH=CH2The addition that stop in alkene stage can be syn or anti H H H3C HC=C C=C CH3CH2CH3H CH2CH3Syn with Lindlar/ catalyst Anti with Na or Li/ NH3 (liquid)
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