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Title: Room Temperature Observation of p-Xylylenes by 1H NMR and Evidence for Diradical Intermediates in Their Oligomerization

Authors:
;
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
883180
Report Number(s):
IS-J 7047
DOE Contract Number:
W-7405-Eng-82
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Organic Chemistry; Journal Volume: 71
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY

Citation Formats

Walter S. Trahanovsky, and Steven P. Lorimor. Room Temperature Observation of p-Xylylenes by 1H NMR and Evidence for Diradical Intermediates in Their Oligomerization. United States: N. p., 2006. Web. doi:10.1021/jo0516279.
Walter S. Trahanovsky, & Steven P. Lorimor. Room Temperature Observation of p-Xylylenes by 1H NMR and Evidence for Diradical Intermediates in Their Oligomerization. United States. doi:10.1021/jo0516279.
Walter S. Trahanovsky, and Steven P. Lorimor. Sun . "Room Temperature Observation of p-Xylylenes by 1H NMR and Evidence for Diradical Intermediates in Their Oligomerization". United States. doi:10.1021/jo0516279.
@article{osti_883180,
title = {Room Temperature Observation of p-Xylylenes by 1H NMR and Evidence for Diradical Intermediates in Their Oligomerization},
author = {Walter S. Trahanovsky and Steven P. Lorimor},
abstractNote = {},
doi = {10.1021/jo0516279},
journal = {Journal of Organic Chemistry},
number = ,
volume = 71,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • A crystalline phase of the title diradical has been prepared and characterized by X-ray diffraction, IR, UV-vis, and EPR spectroscopies, and magnetic susceptibility measurements. This phase belongs to the C2/c space group [a = 16.57(2) {angstrom}, b = 16.116(2) {angstrom}, c = 13.10(1) {angstrom}, {beta} = 123.05(4){degrees}, V = 2931(4) {angstrom}{sup 3}, Z = 4, d{sub calc} = 1.30 g cm{sup {minus}3}, T = 21{degrees}C, R{sub u} = 0.092, R{sub w} = 0.116]. The molecular structure of the diradical is characterized by an asymmetrical Z-shaped conformation. The most relevant features observed in the molecular packing are the large interdiacetylene separationsmore » - the shortest one is 8.285 {angstrom}-and the alternation in the characteristics of the intermolecular contacts between the radical side groups of the DA; which are jointed by hydrogen bonds between the oxygen atoms of NO groups and aromatic hydrogen atoms. On the basis of accepted structural criteria, this solid-state structure should not support a single-crystal topochemical polymerization and, accordingly, the UV-induced polymerization is not achieved. Thermal treatment, however, turns the crystals from blue to dark brown. Thermal analyses under nitrogen, performed with DSC and TGA techniques, reveal an explosive and complex decomposition, at temperatures higher than 90{degrees}C, with an evolution of gaseous NO (GC-MS) and a destruction of most of the radical centers of diradical molecules, as demonstrated by EPR and magnetic measurements. The study of the temperature dependence of the EPR signals of very diluted solutions of diradical 1 shows that it has a thermally modulated intramolecular exchange interaction due to the flexibility of the spacers joining the two radical centers and, furthermore, that when this diradical adopts a rigid conformation the two radical moieties are magnetically isolated (J{sup intra}/k {approximately} 0 K). 44 refs., 12 figs., 3 tabs.« less
  • In this communication, we report the femtosecond time-resolved IR spectroscopic study of the C-H bond activation reaction of Tp{sup *}Rh(CO){sub 2} (Tp{sup *} = HB-Pz{sub 3}{sup *}, Pz{sup *} = 3,5-dimethylpyrazolyl) in room temperature alkane solution. The relatively high C-H activation quantum yield of 30% for this compound has enabled us to detect several very short-lived transient intermediates that are formed during the overall C-H bond activation process. These experiments were performed with our recently completed 30 Hz femtosecond IR spectrometer with 200 fs time resolution. Our experiment represents the first direct observation of the reactive solvated monocarbonyl intermediate speciesmore » that form in the C-H oxidative addition reactions at room temperature in alkane solution. A summary of our results is shown. 23 refs., 3 figs.« less
  • Upon heating, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17). Solution pyrolysis of 4 in inert aromatic solvents produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocyclooctene (9), and o-allyl-n-propylbenzene (10), in high yield. When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent, high yields of the reduced product o-di-n-propylbenzene (12) are obtained. The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent establish that 2,3-di-n-propyl-1,4-dehydrobenzene is a discrete intermediatemore » on the pathway leading to products. When the reaction was run in the heated probe of an NMR spectrometer, CIDNP was observed in 10. This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by sequential intramolecular [1,5] hydrogen transfer, on the pathway to products. The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicate a biradical description of these molecules. Biradical 17 has been estimated to have a lifetime of about 10 -9 s at 200°C and to lie in a well of about 5 kcal/mol with respect to the lowest energy unimolecular pathway ([1,5] hydrogen transfer). Ring opening (expected to be the lowest energy process for 1,4-dehydrobenzenes in which intramolecular hydrogen transfer is unlikely) to the isomeric diethynyl olefin 7 appears to have an activation enthalpy of about 10 kcal/moL Upon thermal reaction in the gas phase (400°C) or in solution in inert solvents (Z)-hexa-2,3-diethyl-1,5-diyn-3-ene (5) rearranges in good yield to the isomeric diethynyl olefin (Z)-deca-3,7-diyn-5-ene (8) again presumably via 2,3-diethyl-1,4-dehydrobenzene 20 (addition of 1,4-cyclohexadiene to the reaction solution leads to a good yield of o-diethylbenzene, the expected trapping product of biradical 20). In conclusion, the absence of products due to intramolecular [1,4] hydrogen transfer indicates that this process is at least one or two orders of magnitude slower than [1,5] hydrogen transfer in 17. At 500°C in the gas phase products due to [1,4] hydrogen transfer begin to appear.« less
  • Upon being heated, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17). Solution pyrolysis of 4 in inert aromatic solvents produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocycloctene (9), and o-allyl-n-propylbenzene (10), in high yield. When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent high yields of the reduced product o-di-n-propylbenzene (12) are obtained. The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent pyl-1,4-dehydrobenzene is a discrete intermediate onmore » the pathway leading to products. When the reaction was run in the heated probe of an NMR spectrometer, chemically induced dynamic nuclear polarization was observed in 10. This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by sequential intramolecular (1,5) hydrogen transfer, on the pathway to products. The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicates a biradical description of these molecules.« less
  • Previous X-ray Diffraction (XRD) and Nuclear Magnetic Resonance (NMR) studies on Ti-doped NaAlH{sub 4} revealed the reaction products of two heavily doped (33.3 at.%) samples that were solvent-mixed and mechanically-milled. This investigation revealed that nano-crystalline or amorphous Al{sub 2}O{sub 3} forms from the possible coordination of aluminum with oxygen atom of the furan ring system from added tetrahydrofuran (THF) in the solvent-mixed sample, and that TiAl{sub 3} forms in mechanically-milled samples. The present paper provides a more sophisticated NMR investigation of the these materials. On heavily doped (33.3 at.%) solvent-mixed samples, {sup 27}Al Magic Angle Spinning (MAS) NMR {sup 27}Almore » multiple quantum MAS (MQMAS) indicates the presence of an oxide layer of Al{sub 2}O{sub 3} on the surfaces of potentially bulk nanocrystalline Ti, nanocrystalline TiAl{sub 3}, and/or metallic aluminum. The {sup 1}H MAS NMR data also indicate the possible coordination of aluminum with the oxygen atom in the THF. On heavily doped samples that were mechanically milled, {sup 27}Al MAS NMR and static NMR confirms the presence of TiAl{sub 3}. In addition, the {sup 1}H MAS NMR and {sup 1}H spin-lattice relaxation (T{sub 1}) measurements are consistent with the presence of TiH{sub 2}. These results are in agreement with recent XAFS measurements indicating both Al and H within the first few coordination shells of Ti in the doped alanate.« less