Abstract
Elimination reactions of (E)- and (Z)-benzaldehyde O-benzoyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The rate of elimination from 2 is approximately 36000 fold faster than that from 1. For reactions of 1 with DBU in MeCN, kH/kD = 3.3 ± 0.2, Hammett ρ value of 2.19 ± 0.05, β1g = -0.49 ± 0.02, ΔH‡ = 10.4 ± 0.6 kcal/mol, and ΔS‡ = -34.3 ± 2.6 eu have been determined. The corresponding values for 2 are kH/kD = 7.3 ± 0.2, ρ = 1.21 ± 0.05, β1g = -0.40 ± 0.01, ΔH‡ = 6.8 ± 0.5 kcal/mol, and ΔS‡ = -25.8 ± 1.9 eu, respectively. The results indicate that the anti-eliminations from 2 proceed via more symmetrical transition states with smaller degrees of proton transfer and Nα-OC (O)Ar bond cleavage, less negative charge development at the β-carbon, and a greater extent of triple bond formation than that for the syn-elimination.
| Original language | English |
|---|---|
| Pages (from-to) | 4685-4690 |
| Number of pages | 6 |
| Journal | Journal of Organic Chemistry |
| Volume | 63 |
| Issue number | 14 |
| Publication status | Published - 1998 Jul 10 |
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- Organic Chemistry
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Elimination Reactions of (E)- and (Z)-Benzaldehyde O-Benzoyloximes. Transition State Differences for the Syn- and Anti-Eliminations Forming Nitriles. / Cho, Bong-Rae; Chung, Hak Suk; Cho, Nam Soon.
In: Journal of Organic Chemistry, Vol. 63, No. 14, 10.07.1998, p. 4685-4690.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Elimination Reactions of (E)- and (Z)-Benzaldehyde O-Benzoyloximes. Transition State Differences for the Syn- and Anti-Eliminations Forming Nitriles
AU - Cho, Bong-Rae
AU - Chung, Hak Suk
AU - Cho, Nam Soon
PY - 1998/7/10
Y1 - 1998/7/10
N2 - Elimination reactions of (E)- and (Z)-benzaldehyde O-benzoyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The rate of elimination from 2 is approximately 36000 fold faster than that from 1. For reactions of 1 with DBU in MeCN, kH/kD = 3.3 ± 0.2, Hammett ρ value of 2.19 ± 0.05, β1g = -0.49 ± 0.02, ΔH‡ = 10.4 ± 0.6 kcal/mol, and ΔS‡ = -34.3 ± 2.6 eu have been determined. The corresponding values for 2 are kH/kD = 7.3 ± 0.2, ρ = 1.21 ± 0.05, β1g = -0.40 ± 0.01, ΔH‡ = 6.8 ± 0.5 kcal/mol, and ΔS‡ = -25.8 ± 1.9 eu, respectively. The results indicate that the anti-eliminations from 2 proceed via more symmetrical transition states with smaller degrees of proton transfer and Nα-OC (O)Ar bond cleavage, less negative charge development at the β-carbon, and a greater extent of triple bond formation than that for the syn-elimination.
AB - Elimination reactions of (E)- and (Z)-benzaldehyde O-benzoyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The rate of elimination from 2 is approximately 36000 fold faster than that from 1. For reactions of 1 with DBU in MeCN, kH/kD = 3.3 ± 0.2, Hammett ρ value of 2.19 ± 0.05, β1g = -0.49 ± 0.02, ΔH‡ = 10.4 ± 0.6 kcal/mol, and ΔS‡ = -34.3 ± 2.6 eu have been determined. The corresponding values for 2 are kH/kD = 7.3 ± 0.2, ρ = 1.21 ± 0.05, β1g = -0.40 ± 0.01, ΔH‡ = 6.8 ± 0.5 kcal/mol, and ΔS‡ = -25.8 ± 1.9 eu, respectively. The results indicate that the anti-eliminations from 2 proceed via more symmetrical transition states with smaller degrees of proton transfer and Nα-OC (O)Ar bond cleavage, less negative charge development at the β-carbon, and a greater extent of triple bond formation than that for the syn-elimination.
UR - http://www.scopus.com/inward/record.url?scp=0000044590&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0000044590&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0000044590
VL - 63
SP - 4685
EP - 4690
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 14
ER -