Photolysis of matrix isolated 1,3-cyclohexadiene, cis-1,3,5-hexatriene, and trans-1,3,5-hexatriene

Datta, Pabitra; Goldfarb, Theodore D.; Boikess, Robert S.

doi:10.1021/ja00749a037

Cited by 22 publications

(9 citation statements)

References 2 publications

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“…Therefore, only the Z-type of ketene isomers (note the Z-orientations around the green double bonds in Scheme ) was here considered as candidates for photoproducts 5a and 5b . There is experimental evidence that 1,3-CHD converts rapidly to Z-1,3,5-HT and slowly to E-1,3,5-HT. , Apparently, a slow accumulation of the E-isomer of open-ring carvacrol is not competitive with other observed UV-induced isomerizations and other exit channels (decarbonylation, see below).…”

Section: Resultsmentioning

confidence: 99%

“…There is experimental evidence that 1,3-CHD converts rapidly to Z-1,3,5-HT and slowly to E-1,3,5-HT. 33,34 Apparently, a slow accumulation of the E-isomer of open-ring carvacrol is not competitive with other observed a Note that the substituents of the starting form (top-left) have indexes 3 and 5 corresponding to the ring positions where they occur. In the entire scheme, these indexes (R 3 , R 5 ) are kept the same.…”

Section: Ring Contraction To the Dewar Isomermentioning

confidence: 99%

“…To the best of our knowledge, only a few monomeric monoterpenes have been objects of photochemical studies in cryogenic matrices. − Among these, α-terpinene and α-phellandrene , have the closest structural proximity with carvacrol. They represent alkyl-substituted derivatives of 1,3-cyclohexadiene (1,3-CHD, see Scheme ), and their main photochemical reactions resemble the photochemistry of 1,3-CHD, which consists of a ring-opening reaction with production of the respective 1,3,5-hexatriene (1,3,5-HT) or its alkyl-substituted analogues. − …”

Section: Introductionmentioning

confidence: 99%

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Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix

2021

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In this work, monomers of carvacrol (5-isopropyl-2-methylphenol), a natural monoterpene exhibiting wide range bioactivity, were trapped in a cryogenic argon matrix and characterized by infrared spectroscopy, while quantum chemical calculations at the B3LYP and MP2 levels were employed to characterize the conformational landscape of the isolated molecule. Four conformers have been localized on the potential energy surface, and the factors accounting for their relative stability were analyzed. The two most stable conformers of carvacrol, differing in the relative orientation of the isopropyl group and both having the OH group pointing away from the vicinal methyl fragment, were identified in the cryomatrix for the first time. The individual spectral signatures of the two conformers were distinguished based on the change in their relative abundance induced by exposing the matrix to broadband infrared light. Matrix-isolated carvacrol was also irradiated with broadband UV light (λ > 200 nm), which resulted in the cleavage of the OH group. Recombination of the released H atom at the ortho- or para-position of the ring resulted in the formation of alkyl-substituted cyclohexadienones. These were found to undergo subsequent valence and open-ring isomerizations, leading, respectively, to the formation of a Dewar isomer and open-chain conjugated ketenes. Decarbonylation of the photoproducts was also observed for longer irradiation times. A mechanistic analysis of the observed photochemical transformations is presented.

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Section: Resultsmentioning

confidence: 99%

Section: Ring Contraction To the Dewar Isomermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix

2021

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“…The rate indicated for E-hexatriene is from a measurement at high excess energy [23]. The barrier was drawn higher for this molecule than for the Z isomer, since for the former the photoisomerization in a cold matrix does take place, whereas for the latter it is frozen [24]. Table 1 compares the 1 B and 2A lifetimes for the different molecules.…”

Section: Hexatriene: Several Separate 2 a Minima And Conical Intersecmentioning

confidence: 99%

Ultrafast photochemical pericyclic reactions and isomerizations of small polyenes

Fuß

Hering

Kompa

et al. 1997

Ber Bunsenges Phys Chem

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Potential energy surfaces for pericyclic reactions can easily be predicted by means of correlation diagrams. Whereas the initially excited state (called 1 B in this paper) may vary from molecule to molecule, its population is collected by a lower, dark state (2A) of always the same nature, which corresponds to a two‐electron excitation. From there, the system leaves to the ground states of educt and product(s) via a conical intersection (CI). Using transient absorption and transient ionization spectroscopy, we measured the lifetimes t1B and t2A of these states after initiating electrocyclic ring opening of 1,3‐cyclohexadiene and some of its derivatives (α‐terpinene, α‐phellandrene and 7‐dehydrocholesterol). t2A can be considered the reaction time constant. Whereas t2A = 5.2 ps for dehydrocholesterol. it is 80–100 fs for the other three molecules. We suggest that the former system needs some time to find the exit (the CI) from the 2A surface, whereas in the latter cases the CI is located right in the line of the steepest descent. We apply the same scheme to, and compile the time constants for, some other fast processes: the [1.3] sigmatropic reactions of norbornene and norbornadiene (t2A = 220 and 210 fs) and the fast internal conversions of cycloheptatriene (80 fs) and several UV stabilizers. The latter two processes are suggested to take the same pathway as the pericyclic hydrogen shifts in these molecules. We also point out the similarity of the pericyclic potential surfaces to those of cis‐trans isomerizations and give evidence that cis‐stilbene (t2A < 300 fs), too, is accelerated directly in the direction of the CI. For cis‐trans isomerization of longer polyenes there are however several 2A minima and conical intersections. We also give examples where additional branchings and competing reactions play a role.

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“…37,40 That explanation did not consider the efficient regioselective cis → trans photoisomerization at C 1 C 2 of 1-cis-deuterio-trans-1,3-pentadiene, 41 which Squillacote attributed to an allyl cation-methylene anion intermediate following Dauben's lead 42 and Salem's sudden polarization theoretical prediction. 43, 44 1,3-Bond formation was proposed to yield an unstable product on irradiation of c-Ht at 20 K in an argon matrix 45 whose formation via the calculated "kink" CI 21,22 is plausible. It was suggested 34,35 that, following S 2 (1 B) → S 1 (2 A) decay in the femtosecond time scale, S 1 → S 0 radiationless decay to the original ground state occurs very fast via a barrierless process involving a "non-totally symmetric deformation of the molecular backbone" that provides access to the "kink" CI.…”

Section: ■ Introductionmentioning

confidence: 99%

Photochemistry of the 1,6-Dideuterio-1,3,5-hexatrienes in Solution: Efficient Terminal Bond Photoisomerization in One-Bond-Twist and Bicycle Pedal Ways

et al. 2018

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The report that the central bond photoisomerization of the 1,3,5-hexatrienes (Hts) is highly inefficient has encouraged theoreticians to seek conical intersections (CIs) at geometries that can explain rapid nonradiative return to the initially excited isomer. Because they are photochemically silent, torsional relaxations about the terminal double bonds of the Hts have not been evaluated as significant radiationless decay pathways. Study of the photoisomerization of trans,trans,trans- and trans,cis,trans-1,6-dideuterio-1,3,5-hexatrienes (ttt- and tct-Htd2) addresses this issue. Degassed cyclohexane-d 12 (C6D12) and CD3CN solutions were irradiated at 254 nm in quartz NMR tubes, and the progress of the reactions was followed by 1H NMR. Photoisomerization rates based on the integration of terminal hydrogen NMR peaks are in reasonable agreement with rates obtained by fitting pure isomer NMR spectra to the phase shift and baseline corrected experimental NMR spectra. The results show that terminal bond isomerization is highly efficient, especially when one considers that central bond isomerization is much more efficient than previously reported and is mainly observed together with terminal bond isomerization. A mechanism involving terminal one-bond-twist (OBT) in competition with a bicycle pedal (BP) process accounts for all terminal and most central bond photoisomerization. OBT central bond isomerization is a minor reaction that is observed primarily in the tct to ttt direction. Most surprising is the prominent role of the BP process in central bond photoisomerization. Proposed initially to account for photoisomerization in free volume constraining media, it is observed here in the absence of medium constraints.

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Photolysis of matrix isolated 1,3-cyclohexadiene, cis-1,3,5-hexatriene, and trans-1,3,5-hexatriene

Cited by 22 publications

References 2 publications

Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix

Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix

Ultrafast photochemical pericyclic reactions and isomerizations of small polyenes

Photochemistry of the 1,6-Dideuterio-1,3,5-hexatrienes in Solution: Efficient Terminal Bond Photoisomerization in One-Bond-Twist and Bicycle Pedal Ways

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