ALKYNES - Chapter 7 nomenclature - (chapt 5), structure, classification acidity of terminal acetylenes - (chapt 4) alkylation prep - dehydrohalogenation (-2HX) or double -elimination reduction - H2/M (chapt 6) and chemical hydroboration (chapt 6) - protonation - oxidation (hydration) enol-keto tautomerism addition of Hg++, HX, X2, H2O (chapt 6) synthesis (chapts 6) ss25 18 [blue - chemistry from previous chapters]

synthesis but first …… nomenclature - structure, classification Chapter 7 synthesis nomenclature - structure, classification acidity of terminal acetylenes ) alkylation -elimination reduction - H2/M & chemical hydroboration - protonation - oxidation enol-keto tautomerism addition: Hg++/H2O, HX, X2 synthesis but first ……

synthesis nomenclature - structure, classification Chapter 7 synthesis nomenclature - structure, classification acidity of terminal acetylenes ) alkylation -elimination reduction - H2/M & chemical hydroboration - protonation - oxidation enol-keto tautomerism addition: Hg++/H2O, HX, X2 synthesis

Structure - two general types acetylene, ethyne C H Structure - two general types (1) internal - R and R’ = alkyl, Aryl, etc. C R R' (2) terminal - R = alkyl, Aryl, etc. <-- creates additional chemistry 8,28

Alkyne Nomenclature Common: alkyl alkyl' acetylene C R’ R

Nomenclature: IUPAC - longest chain containing the most important functional group(s) = root #-alkyne 4-chloro-6-cyclohexyl-5-methyl-2-hexyne add substituents with #’s

R-C-C-R’  -bond 180o bond angle Acetylene - linear geometry - sp hybridization 180o bond angles 90o angle  bond to  orbitals)ß C R’ R R-C-C-R’  -bond 180o bond angle

Name: ______________ seat: ____ Write the product(s) of the following reactions.

Acidity of organic compounds H C CH 3 > pKa = 44 H-Csp2 H C CH 3 > pKa = 50 H-Csp3 H C CH 3 pKa = 25 H-Csp Why ? recall chapter 4 The more s-character, the more acidic the C-H bond 50% 33% 25%

Relative basicity (acidity) also - NH2 H-NH3

Acid-Base reactions organometallic reagent (15)

last Thursday: Acid-Base reactions R' = alkyl = D

Alkylation of Acetylides Recall RX type: substitution acetylide anions undergo substitution rx with 1o alkyl halides form new C-C bonds termed “alkylation”

Alkylation of Acetylides How do we make the anions of acetylenes?

Alkylation of Acetylides

Alkylation of Acetylides Acetylide anions - 2° and 3° halides: -eliminates (strong base, reverse of addition) no alkylation 2°R-X

Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

NOTE! alkenes are sources of diBrs Preparation: Dehydrohalogenation (-2 HX) NOTE! alkenes are sources of diBrs two -eliminations 2 arrangements of diBrs => same acetylene

Reactions - several like C=C - additions A. Reduction - addition of hydrogen syn addition (2x)

Reactions - several like C=C - additions A. Reduction - addition of hydrogen With choice of catalyst - stop at olefin (add 1 eq H2). [Lindlar cat.] syn addition (2x)

Chemical reduction of a triple bond. Nao (liq.) NH3 ether (cosolvent) C H 3 CH C H 3 CH trans olefin for internal acetylenes “mechanism” - Na donates e’s, know rx as prep for trans olefins

Acetylene chemistry - recall olefin chemistry R = H, alkyl

Hydroboration of an internal alkyne terminal

Terminal acetylene hindered borane adds once di-sec-isoamylborane or HB(sia)2

Terminal acetylene hindered borane adds once di-sec-isoamylborane or HB(sia)2 tautomerism H+ transfer (O to C)

internal with oxidation - ketone C O H R R' ketone keto C R R' BH 2 H + H 2 O NaOH enol

regiochemistry

enol-keto tautomerism H+ transfer C  O from HB/[O] Hg+2/H2O other rxs mechanism e(-) arrows or

Hydration of acetylenes terminal yne - HBR2/[O]  aldehyde - Hg++/H2O  ketone internal yne - “either”  ketone(s)

Assume bromonium (chloronium) ion ( like alkene X2 addition ) electrophilic additions Br2 / Cl2 C R R' Br 2 1 eq. Br 2 1 eq. or XS C R R' Assume bromonium (chloronium) ion ( like alkene X2 addition ) Mechanism for 1st addition of X2 C R' R X C R' R X C R' R X

addition of HX vinyl bromide 2o-vinyl R+ R' Br R' Br R' HBr HBr C C 1 eq. or XS C H R' HBr 1 eq. 2o-vinyl R+

addition of HX - second addition HBr 1 eq. C Br H R' C Br H R' HBr 1 eq. or XS 2o carbocation with resonance C Br H R' C Br H R' Br(-) 1o carbocation and no resonance! C Br H R'

How could the vinyl bromide be converted into the Z-olefin How could the vinyl bromide be converted into the Z-olefin? Use any number of reactions but show all necessary reagents and expected products of each step. how? a. H2/Lindlar(cat.) how? Na+-NH2 or b. (1)BH3, (2)AcOH/∆

convert 2-bromopropene to 2-hexanone

convert 2-bromopropene compare carbon skeleton functional groups convert 2-bromopropene to 2-hexanone

compare carbon skeleton functional groups

other way?