CH09 Instructor Notes

CH09 Instructor Notes - Chapter 9 Alkynes I. Nomenclature...

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Ch 221, Chapter 9, Lecture Notes page 1 of 5 Chapter 9 — Alkynes I. Nomenclature Same as alkanes, but use suffix –yne, e.g. hexane -> 1-hexene -> 1-hexyne II. Structure of Alkynes A. Terminal alkynes: R-C C-H B. Internal alkynes: R-C C-R' C. Bonding: Figure 9-2 HCCH sp hybridized 2 π + 1 σ 1.20Å 1.06Å C: 50% s; 50%p Terminal Acetylenes are acidic: Table 9-1 %s character in C-H Bonds pK a (= - log K a ) Ethane 25 62 Ethene 33 45 Ethyne 50 26 HCC CC H H H C H H H negative charge in sp HO negative charge in sp 2 HO negative charge in sp 3 HO A strong base is still needed to deprotonate an alkyne: HO + K H 2 O + pKa = pKa = K = 10 - /10 - = -
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Ch 221, Chapter 9, Lecture Notes page 2 of 5 III. Acetylenes as nucleophiles HH alkylation RH alkylation RR ' Alkylation works will only for methyl and 1°RX, 2° and 3°RX give elimination Examples: HC CH 1) NaNH 2 2) CH 3 Br (1°) HC CCH 3 1) NaNH 2 2) CH 2 CH 3 I (1°) 3 C H 2 H 3 C C Br + HC CH + + Br - IV. PREPARATION OF ALKYNES BY ELIMINATION R H H X X R' 2 NaNH 2 ' Geminal dihalide We've seen this before,
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CH09 Instructor Notes - Chapter 9 Alkynes I. Nomenclature...

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