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Conformations
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The bulky tert-butyl group leads to a large amount of A-strain when that group is in the axial position. The 1,3-interaction of the axial tert-butyl group with the axial hydrogen atoms is apparent in the molecular model. When the tert-butyl group is in the equatorial position, however, three hydrogen atoms are in the axial position, the bulky tert-butyl group is in the equatorial position, and there is no A-strain. Therefore, the equilibrium constant for the equilibrium is large and in favor of the chair conformation with the tert-butyl groups in the equatorial position. In general, the lowest energy conformation will predominate for any given cyclic alkane. In this case, the energy difference is so large, that there is much less than 1% of the axial conformation is present at equilibrium.
Telechelics by Free Radical Polymerization Reactions
Published in Eric J. Goethals, Telechelic Polymers: Synthesis and Applications, 2018
that initiate without losing carbon dioxide except for R = tert butyl. Using 14C-labeled dicyclohexylperoxy dicarbonate and employing a tracer technique for end-group analysis, Razuvaev et al.28 have demonstrated that the primary radical ROCOO· formed by the decomposition of the initiator reacts with monomers such as styrene and MMA much faster than it undergoes decarboxylation, and thus, the RO· radical plays a minor role in initiation. In the polymerization of the ethylene carbonate end-groups, but no fragments originating from the incorporation of RO· could be detected with R = methyl, ethyl. With R = tert butyl, the loss of carbon dioxide resulted in the formation of tert butoxy radicals that are cleaved to methyl radicals before initiation.63
Fabrication, Functionalisation and Surface Modification
Published in Satyendra Mishra, Dharmesh Hansora, Graphene Nanomaterials, 2017
Satyendra Mishra, Dharmesh Hansora
Graphene-based hybrid polymer nanocomposites have been prepared by various methods such as solution blending (e.g. PVA/GO, PAA/GO, PAN/GO), melt mixing (e.g. PMMA/graphene, PP/graphene, PC/graphene), and in situ polymerisation (e.g. PMMA/GO, PP/GO, PE/graphene) [270]. The atom transfer radical polymerisation (ATRP) method has also been employed to graft poly(tert-butyl acrylate) (PtBA) from GO. The GO was reacted with trichloro(4-chloromethylphenyl) silane to prepare the ATRP initiator-coupled GO nanosheets. The modified GO particles were then used as the initiator in the polymerisation of PtBA to give GO nanosheets with covalently grafted PtBA. The grafted hydrophobic polymer brushes produced a substantial enhancement of GO solubility in organic solvents, and the GO-g-PtBA nanosheets formed a stable dispersion in toluene. The functionalised GO nanosheets were successfully integrated into an electroactive polymer matrix and subsequently a composite material based on a thin film of poly(3-hexylthiophene) (P3HT) containing 5 wt% GO-g-PtBA in an Al/GO-g-PtBA+P3HT/indium tin oxide (ITO) sandwich structure, where bi-stable electrical conductivity switching behaviour and a nonvolatile electronic memory effect were observed. Finally, water-dispersible GO-g-poly(acrylic acid) (PAA) nanosheets were prepared by hydrolysis, allowing gold NP-decorated GO-g-PAA nanofilms to be prepared from aqueous dispersions (Fig. 2.16)[274–290, 292, 293].
Organocatalysis with carbon nitrides
Published in Science and Technology of Advanced Materials, 2023
Sujanya Maria Ruban, Kavitha Ramadass, Gurwinder Singh, Siddulu Naidu Talapaneni, Gunda Kamalakar, Chandrakanth Rajanna Gadipelly, Lakshmi Kantham Mannepalli, Yoshihiro Sugi, Ajayan Vinu
Cu-incorporated g-CN was successfully employed for the simultaneous oxidation and amidation in one reaction step in the liquid phase with excellent activity, reusability, and a simple workup method [139]. The reaction proceeds through a free radical mechanism in the presence of a Cu/g-CN catalyst and tert-butyl hydroperoxide as an oxidizing agent. In similar research work, Gafuri et al. have studied the oxidative amidation tandem reaction employing the Cu(II)‑β‑cyclodextrin immobilized on g-CN nanosheets as a highly effective catalyst. The oxidative amidation was accomplished in a single step. The reaction proceeds through a free radical mechanism with hemiaminal intermediate in the presence of activated tert-butyl peroxy radical [140]. Epoxidation of trans-stilbene to trans-stilbene oxide was also effectively catalyzed by bimetallic clusters (Fe, Pd, and Ir) supported on the mesoporous g-CN catalysts in the liquid phase. These catalysts showed superior conversion of the substrate and selective formation of the epoxide which was attributed to the formation of active oxygen species [141]. Han and colleagues have also reported the oxidation of toluene to benzaldehyde catalyzed by Cu and B doped g-CNs by tert-butyl hydroperoxide (TBHP) oxidizing agent [142]. The presence of the redox cycle created by these metal ions facilitates free-radical oxidation which helps in achieving excellent catalytic performance.
DFT investigates the mechanisms of cross-dehydrogenative coupling between heterocycles and acetonitrile
Published in Molecular Physics, 2022
Cheng-Yu He, Hong-Xia Hou, Ming-Qiong Tong, Da-Gang Zhou, Rong Li
Cross-dehydrogenative coupling (CDC) is always used to construct new C–C bonds in synthetic organic chemistry, which is efficient, atom economic, and environment-friendly [1–4]. And its core reaction is C–H activation. Generally, C–H activation represents a universal means to fabricate desirable products without prefunctionalising reactants because C–H bonds are ubiquitous in organics. However, C−H activation is fairly challenging due to the inertia of C−H bonds and the poor selectivity. To overcome this, diverse strategies have been adopted, including harsh experimental conditions, transition metal catalysis, and metal surfaces. The free radical chemistry with a high activity of a single electron could provide new thinking to activate the inert C–H bond in organic chemistry, and many radical initiators, such as tert-butyl-hydroperoxide (TBHP) [5], di-tert-butyl peroxide (DTBP) [6], benzoyl peroxide (BPO) [7], bis(4-tert-butyl cyclohexyl)peroxy dicarbonate (TBCP) [8], tert-butylperoxybenzoate (TBPB) [9] and dicumyl peroxide (DCP) [10], can be used to generate radicals to activate the C–H bond. For example, Pan and his coworkers employed DCP to activate Csp3-H to synthesise quinazolinones and their derivatives in Scheme 1(a) [10]; and Yan and his cooperators took TBPB as the radical initiator to achieve the Csp3-H activation in Scheme 1(b) [11].
Carbazolyl-bis(triazole) and Carbazolyl-bis(tetrazole) Complexes of Palladium(II) and Platinum(II)
Published in Journal of Coordination Chemistry, 2021
Samya Samanta, Cameron Zheng, Leah Gajecki, David J. Berg, Allen G. Oliver, Tristan Crosby, Logan Godin, Jaylene Sandhu
Several of the structures showed disorder in one or more of the carbazole tert-butyl groups (5b, 5c, 8b and 9b) and in one case, in a tetrazole isopropyl substituent (8b). In the case of 5b and 5c, one tert-butyl group showed the typical hexagonal arrangement of rotational disorder. Such rotational disorder in tert-butyl groups is not unusual. This disorder was satisfactorily modelled for 5b, 5c and 9b by splitting the methyl carbon positions along the longest ADP axis into two groups with their occupancies linked through a free variable that was refined. Complex 8b showed similar disorder in one carbazole tert-butyl substituent in each of two independent molecules in the asymmetric unit and in one isopropyl substituent on a tetrazole ring. Initially the disordered components were modeled with occupancies set at 50%. Inspection of the model revealed that this ratio held true for one disordered tert-butyl unit and the isopropyl group. However, one tert-butyl showed that the occupancy was not this simple. The methyl carbon atoms of this group (C18–C20) were refined with occupancies initially summed to unity that yielded a near 0.8:0.2 ratio. In the final model these occupancies were fixed at 0.8:0.2. Bond distance restraints were applied to the C–C bond distances for this tert-butyl group, and the displacement parameters of all of the disordered tert-butyl carbon atoms, including the quaternary carbon, had restraints applied.