Trimethylene characterized

Singlet diradicals are usually extremely short-lived intermediates. For example, trimethylene (TM, 2) was observed to have a fast decay time of 120 fs by femtosecond spectroscopy [84, 85]. Since the localized 1,3-cyclopentanediyl diradical (62) was characterized by Buchwalter and Closs in 1975 [81, 82], experimental efforts have been made to prepare and characterize the persistent, localized singlet 1,3-diradicals. Some experimental achievements of the localized diradicals are collected in Fig. 25 and Table 3. It should be mentioned that the literature of experimental studies selected here is not exhaustive and more related references can be found in [83-115] and others. 

These new derivatives were isolated in good yields (60-94%) as high boiling liquids and were fully characterized by NMR spectroscopy (1H, 13C, and 11B) and elemental analysis. The proton NMR of the starting material 1 shows a well-resolved multiplet and quintet for the trimethylene bridge. Upon monosubstitution, however, three complex multiplets are observed, indicative of the unsymmetrical structures of these derivatives. Also, the nonequivalence of the N-C carbon atoms is clearly apparent in the 13C NMR spectra of 2-4. 

For example, the distonic anion radical of cyclopentadienylidene trimethylen-emethane reacts under mass spectrometer gaseous-phase conditions with carbon disulfide by sulfur abstraction and with nitric oxide by NO-radical addition. The first reaction characterizes the distonic anion radical mentioned as a nucleophile bearing a negative charged moiety. The second reaction describes the same anion radical as a species having a group with radical unsaturation (Zhao et al. 1996). 

More recently, the radical cation of the parent system has been characterized by ESR/ENDOR spectroscopy [340], These experiments revealed medium-sized hfcs for both the bridgehead (—11.4 G) and the equatorial protons (+11.4G) and large positive hfcs (+ 77 G) for the axial protons (which in 75 are replaced by the trimethylene bridge). The large difference between the couplings of the axial and equatorial protons indicates a nonplanar, puckered geometry of the radical cation. No evidence for interconversion is apparent up to 160 K this finding requires an inversion barrier of at least 12 kJ mol-1. 

As a final suggestion for future research, cyclobutanones have also provided the organic photochemist with the opportunity of investigating the existence of unusual and reactive intermediates oxacarbenes, trimethylene biradicals, trimethylenemethane biradicals, acyl alkyl biradicals, and ketenes. Evidence for the intervention of oxacarbenes in the ring-expansion reaction is quite compelling however, their unusual behavior relative to "typical" carbenes (e.g., failure to form cyclopropane adducts with some olefinic substrates) makes them prime subjects for further study and characterization. Unlike oxacarbenes, the existence of acyl alkyl biradicals (e.g., [30]) is tenuous at best. Ideally,... 

Pioneering work of Dowd on trimethylene methane [142], 1,8-naphthoquinodi-methane diradicals were among the first examples of non-Kekule 7r,7r-diradicals that were found to be persistent in their triplet ground state at cryogenic temperatures and were thoroughly characterized by various spectroscopic methods [143], Time resolved studies of diradicals have provided lifetimes and reactivities of numerous diradical intermediates in solution [144], y-irradiation of CAN, 68, in haloalkane glasses at 77 K yielded radical cation 68 + its electronic absorption spectrum has been obtained and represents first report of absorption spectrum of an ionized diradical [145]. Irradiation at >640 nm converted it into an isomer identical with that formed by ionization of 1,4-dihydro-l,4-ethanonaphtho[l,8-rfe][l,2]diazepine 70, and subsequent irradiation of the radical cation at A > 540 nm. Results identified the photo isomer of 68 + to be 69 + (Scheme 4). 

High molecular weight poly(trimethylene carbonate) PTMC (Mn 300 k g/mol, Mw/Mn 1.46), synthesized, purified, and characterized as described in reference [72] is dissolved in chloroform (3 mg/mL). Thin films are prepared by spin-coating these solutions on cleaned Si wafers at 3,000 rpm (film thickness obtained 25 50 nm). Film thicknesses can be determined by AFM imaging using the scratch method described in Chap. 2 (see also above, hands-on example 47). The enzymatic reaction takes place in situ in the liquid cells filled with lipase solutions (lipase from Thermomyces lanuginosus (EC3.1.1.3, minimum 50,000 units/g purchased from Sigma, U.S.A.) at 37°C for 30 s, 1 min, and 2 min, respectively. 

Yu, F. Zhuo, R. Synthesis, characterization, and degradation behaviors of end-group-functionalized poly(trimethylene carbonate)s. Polym. J. 2003, 35 (8), 671-676. 

Ling, J. Shen, Z. Zhu, W. Synthesis, characterization, and mechanism studies on novel rare-earth calixarene complexes initiating ring-trimethylene carbonate. J. Polym. Sci. A Polym. Chem. 2003, 41 (9), 1390-1399. 

Chen, X. McCarthy, S.P. Gross, R.A. Synthesis, characterization, and epoxidation of an aliphatic polycarbonate from 2,2-(2-pentene-l, 5-diyl)trimethylene carbonate (cHTC) ringopening polymerization. Macromolecules 1997, 30 (12), 3470-3476. 

He, F Jia, H.L., Liu, G Wang, Y.P., Feng, J., and Zhuo, R.Z. (2006) Enzymatic synthesis and characterization of novel biodegradable copolymers of 5-benzyloxy-trimethylene carbonate with l,4-dioxan-2-one. Biomacromolecules,... 

From these results, it can be concluded that, as in the unsubstituted trimethylene, the reactive structure of optimal ISC is characterized by a face-to-face orientation of the radical centers and a CCC angle y slightly smaller than for the triplet minima. As the singlet PES drops steeply for small values of y, the triplet state yields preferably cyclic products. The conditions for optimal ISC are similar for both minima and therefore, the stereochemical differentiation... 

Abstract Poly(trimethylene terephthalate) (PTT) fibers, as a new type of polyester, are characterized by much better resilience and stress/recovery properties than poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). PPT chains are much more angularly structured than PET and PBT chains and such chains can be stretched by up to 15% with a reversible recovery (Ward et al. 1976). These properties make PTT highly suitable for uses in fiber, carpet, textile, film, and engineering thermoplastics applications. 1,3-Propanediol (PDO), as one of the polyester raw materials for PTT, has also attracted interest. 

Yu F, Zhuo R (2004) Synthesis and characterization of OH-Terminated poly(trimethylene carbonate)s by alcohol-initiated ring-opening polymerization in melt bulk without using any catalyst. Polym J 36 28-33... 

Mishra, J.K., Chang, Y.W., and Choi, N.S. (2007) Preparation and characterization of rubber-toughened poly(trimethylene terephthalate) /organoclay nanocomposite. Polym. Et. Sd., 47, 863. 

D. Upadhyay, S. Mohanty, S.K. Nayak, M.R. Parvaiz, B.P. Panda, Impact modification of poly(trimethylene terephthalate)/polypropylene blend nanocomposites fabrication and characterization. Journal of Applied Polymer Science 120 (2) (2011) 932-943. 

Hong J T, Cho N S, Yoon H S, KimT H, Lee D H and Kim W G (2005), Preparation and characterization of biodegradable poly(trimethylene carbonate- -caprolactone)-block-poly(p-dioxanone) copolymers ,/Po/ym Sci Polym Chem, 43(13), 2790-2799. 

Al-Azemi, T.F., Harmon, J.P., Bisht, K.S., 2000. Enz3mie-catalyzed ring-opening copolymerization of 5-methyl-5-benzyloxycarbonyl-l,3-dioxan-2-one (MBC) with trimethylene carbonate (TMC) synthesis and characterization. Biomacromolecules 1, 493—500. 

Buchholz, B., 1993. Analysis and characterization of resorbable DL-lactide-trimethylene carbonate copolyesters. Journal of Materials Science Materials in Medicine 4, 381—388. 

Schnee, G., Fliedel, C., Aviles, T., Dagome, S., 2013. Neutral and cationic N-heterocyclic carbene zinc adducts and the B OH/Zn(C6p5)2 binary mixture — characterization and use in the ring-opening polymerization of 3-butyrolactone, lactide, and trimethylene carbonate. European Journal of Inorganic Chemistry 2013, 3699—3709. 

---