NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene, dibenzo[d,d′]benzo[1,2-b:4,3-b′]difuran, and dibenzo[d,d′]benzo[1,2-b:4,5-b′]difuran in superacidic media
Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran (2), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran...
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Published in | Journal of physical organic chemistry Vol. 29; no. 2; pp. 107 - 111 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Bognor Regis
Blackwell Publishing Ltd
01.02.2016
Wiley Subscription Services, Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran (2), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran (3) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H‐SbF5 (4:1)/SO2ClF and 3 in FSO3H‐SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+, into one benzo[b,d]furan unit for 2aH+, and into one benzo[b,d]furan unit for 3aH+. Copyright © 2015 John Wiley & Sons, Ltd.
The most stable persistent cations derived from the title compounds, 1–3, were found to be 1aH+ with protonation at C(4), 2aH+ with protonation at C(6), and 3aH+ with protonation at C(6) by experimental and theoretical methods. |
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Bibliography: | Supporting info item istex:97AED8F863DC60489AFA0A6782E31D306FC7B5A5 ArticleID:POC3505 ark:/67375/WNG-4F3M9XJC-L |
ISSN: | 0894-3230 1099-1395 |
DOI: | 10.1002/poc.3505 |