Margel Bonifacio - Academia.edu (original) (raw)

Uploads

Papers by Margel Bonifacio

Journal of Physical Organic Chemistry, Apr 1, 2017

Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly... more Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly low Cope rearrangement activation barriers and their close approach to homoaromaticity. The title compounds are unusual in that they do not undergo the Cope rearrangement and are locked as a single tautomer with no evidence whatsoever for the existence of the other "open" tautomer. This total lack of the Cope rearrangement was demonstrated through variable-temperature 13 C NMR spectroscopy and computational studies.

The objective of this project is to prepare polymeric helicenes. These polycyclic aromatic hydroc... more The objective of this project is to prepare polymeric helicenes. These polycyclic aromatic hydrocarbons (PAH)s are attractive synthetic targets not only for academic purposes but also for their potential application in molecular electronics, sensing, and nanodevices. Incorporation of this novel material into a working TNT sensor has been proposed. The preparation of the target compound involves ring-closing metathesis (RCM) of poly(m-phenylene)s with vinyl pendants. Studies on the utility of RCM for the preparation of PAHs were conducted. RCM of 2,4’,6’,2”-tetravinyl-[1,1’;3’,1”]terphenyl and 2,2’,5’,2”-tetravinyl-[1,1’;4’,1’]terphenyl affords in high yield the isomeric [a,j]and [a,h]-dibenzanthracenes, respectively. Calculations show that the RCM of divinyl substituents to give phenanthrene units is exergonic by 28 kcal/mol. The phenanthrene units are thermodynamic sinks, ~27 kcal/ mol more stable than competing products. RCM is a synthetically useful method to generate multiple new benzenoid rings in a single step. While the addition of substituents at the βposition of the vinyl group slows down free radical polymerization, only substrates bearing methyl and n-propyl substituents are considerably active towards RCM. When the RCM product is a thermodynamic sink, the formation of a volatile byproduct, such as ethylene, is not necessary. Poly(m-phenylene)s with styryl, n-pentenyl and n-propenyl pendants at the 4 and 6 position were synthesized from suitable AB-monomers using Suzuki polycondensation in good yields. Gel permeation chromatography analysis gave an average composition of a 22-mer for poly(4,6-di(E)-styryl-m-phenylene), 75-mer for poly(4,6-dipentenyl-m-phenylene), and 107-mer for poly(4,6-di(E)-prop-1-enyl-m-phenylene) based on the Mw values.

The Journal of Organic Chemistry, 2005

Copyright © 2016 John Wiley & Sons, Ltd. Barbaralanes and semibullvalenes are generally fluxional... more Copyright © 2016 John Wiley & Sons, Ltd. Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly low Cope rearrangement activation barriers and their close approach to homoaromaticity. The title compounds are unusual in that they do not undergo the Cope rearrangement and are locked as a single tautomer with no evidence whatsoever for the existence of the other “open” tautomer. This total lack of the Cope rearrangement was demonstrated through variable-temperature 13C NMR spectroscopy and computational studies. Copyright © 2016 John Wiley & Sons, Ltd

Angewandte Chemie International Edition, 2012

Dedicated to Professor Robert G. Bergman on the occasion of his 70th birthday Staab and Diederich... more Dedicated to Professor Robert G. Bergman on the occasion of his 70th birthday Staab and Diederich defined cycloarenes as comprising annelated benzene rings that form a macrocycle with inward-pointing C À H bonds. [1] Their synthesis and characterization of kekulene, the prototypical cycloarene, [1-4] answered a long-standing and fundamental question about arenes and the nature of aromaticity: do p electrons move throughout the entire system, as hypothesized by Pauling, [5] or do they remain localized in rings, as predicted by McWheeny [6] and described phenomenologically by Clar. [7] The chemical shift of the inner protons of 2 gave the answer. Paulings model suggested that kekulene 2 should behave as concentric annulenes (Scheme 1 bottom right), and that the inner protons ought to be strongly shielded, as in [18]annulene. [8] The localized model, as embodied by Clars aromatic sextets, suggests that the ring currents arise from localized rings (Figure 1 top right), and that the inner protons should be deshielded, as in benzene. Experiments showed that the inner protons are deshielded and resonate at d > 7 ppm. This deshielding demonstrates that electrons do not move freely about the entire molecule, but are instead localized into individual rings, just as in benzene. We report the synthesis and properties of kekulenes seven-sided cousin septulene (1), and find that its properties reinforce the conclusions above and open some new questions. Scheme 1. Septulene 1 and kekulene 2. The unique radial double bond in the KekulØ structure of 1 is indicated.

Angewandte Chemie International Edition, 2012

Journal of Physical Organic Chemistry

Journal of Physical Organic Chemistry, Apr 1, 2017

Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly... more Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly low Cope rearrangement activation barriers and their close approach to homoaromaticity. The title compounds are unusual in that they do not undergo the Cope rearrangement and are locked as a single tautomer with no evidence whatsoever for the existence of the other "open" tautomer. This total lack of the Cope rearrangement was demonstrated through variable-temperature 13 C NMR spectroscopy and computational studies.

The objective of this project is to prepare polymeric helicenes. These polycyclic aromatic hydroc... more The objective of this project is to prepare polymeric helicenes. These polycyclic aromatic hydrocarbons (PAH)s are attractive synthetic targets not only for academic purposes but also for their potential application in molecular electronics, sensing, and nanodevices. Incorporation of this novel material into a working TNT sensor has been proposed. The preparation of the target compound involves ring-closing metathesis (RCM) of poly(m-phenylene)s with vinyl pendants. Studies on the utility of RCM for the preparation of PAHs were conducted. RCM of 2,4’,6’,2”-tetravinyl-[1,1’;3’,1”]terphenyl and 2,2’,5’,2”-tetravinyl-[1,1’;4’,1’]terphenyl affords in high yield the isomeric [a,j]and [a,h]-dibenzanthracenes, respectively. Calculations show that the RCM of divinyl substituents to give phenanthrene units is exergonic by 28 kcal/mol. The phenanthrene units are thermodynamic sinks, ~27 kcal/ mol more stable than competing products. RCM is a synthetically useful method to generate multiple new benzenoid rings in a single step. While the addition of substituents at the βposition of the vinyl group slows down free radical polymerization, only substrates bearing methyl and n-propyl substituents are considerably active towards RCM. When the RCM product is a thermodynamic sink, the formation of a volatile byproduct, such as ethylene, is not necessary. Poly(m-phenylene)s with styryl, n-pentenyl and n-propenyl pendants at the 4 and 6 position were synthesized from suitable AB-monomers using Suzuki polycondensation in good yields. Gel permeation chromatography analysis gave an average composition of a 22-mer for poly(4,6-di(E)-styryl-m-phenylene), 75-mer for poly(4,6-dipentenyl-m-phenylene), and 107-mer for poly(4,6-di(E)-prop-1-enyl-m-phenylene) based on the Mw values.

The Journal of Organic Chemistry, 2005

Copyright © 2016 John Wiley & Sons, Ltd. Barbaralanes and semibullvalenes are generally fluxional... more Copyright © 2016 John Wiley & Sons, Ltd. Barbaralanes and semibullvalenes are generally fluxional molecules renowned for their exceedingly low Cope rearrangement activation barriers and their close approach to homoaromaticity. The title compounds are unusual in that they do not undergo the Cope rearrangement and are locked as a single tautomer with no evidence whatsoever for the existence of the other “open” tautomer. This total lack of the Cope rearrangement was demonstrated through variable-temperature 13C NMR spectroscopy and computational studies. Copyright © 2016 John Wiley & Sons, Ltd

Angewandte Chemie International Edition, 2012

Dedicated to Professor Robert G. Bergman on the occasion of his 70th birthday Staab and Diederich... more Dedicated to Professor Robert G. Bergman on the occasion of his 70th birthday Staab and Diederich defined cycloarenes as comprising annelated benzene rings that form a macrocycle with inward-pointing C À H bonds. [1] Their synthesis and characterization of kekulene, the prototypical cycloarene, [1-4] answered a long-standing and fundamental question about arenes and the nature of aromaticity: do p electrons move throughout the entire system, as hypothesized by Pauling, [5] or do they remain localized in rings, as predicted by McWheeny [6] and described phenomenologically by Clar. [7] The chemical shift of the inner protons of 2 gave the answer. Paulings model suggested that kekulene 2 should behave as concentric annulenes (Scheme 1 bottom right), and that the inner protons ought to be strongly shielded, as in [18]annulene. [8] The localized model, as embodied by Clars aromatic sextets, suggests that the ring currents arise from localized rings (Figure 1 top right), and that the inner protons should be deshielded, as in benzene. Experiments showed that the inner protons are deshielded and resonate at d > 7 ppm. This deshielding demonstrates that electrons do not move freely about the entire molecule, but are instead localized into individual rings, just as in benzene. We report the synthesis and properties of kekulenes seven-sided cousin septulene (1), and find that its properties reinforce the conclusions above and open some new questions. Scheme 1. Septulene 1 and kekulene 2. The unique radial double bond in the KekulØ structure of 1 is indicated.

Angewandte Chemie International Edition, 2012

Journal of Physical Organic Chemistry