Bulky Isopropyl Research Articles

Synthesis and Characterization of Diacylthiourea and Diacylthioureato Cu(I) Complexes

A series of six disubstituted diacylthioureas 1,3‐ and 1,4‐C6H4[C(O)NHC(S)NR1R2]2 (L1‐6) were synthesized with varied Rn substituents (R1 = R2 = Et for L1‐2; R1 = R2 = Bn for L3‐4; R1 = iPr and R2 = Ph for L5 (1) and L6 (2)). Treatment of Ln with Cu(I) halide precursors CuX(PPh3)3 (X = Cl, Br, I) produced the discrete binuclear adducts Ln[CuX(PPh3)2]2 (3‐11 and 14‐16; n = 1‐3 and 6) by binding to Cu(I) centres via the monodentate‐S mode. In contrast, L4 and L5 yielded only the chloride products of binuclear L4[CuCl(PPh3)2]2 (12) and mononuclear L5CuCl(PPh3)2 (13), respectively, with one S arm in the latter remaining dangling, while bromide or iodide analogues were not available for L4 and L5, possibly due to the steric hindrance imposed by larger halide anions or bulky isopropyl substituents. The reactions of Ln with nitrate [Cu(NO3)(PPh3)2]led to the double‐deprotonation of ligand protons to generate dianions Ln' (1,3‐/1,4‐C6H4[C(O)NC(S)NR1R2]22‐) and led to the consequent formation of binuclear diacylthioureato Cu(I) complexes Ln'[Cu(PPh3)2]2 (n=1 (17), 2 (18), 4 (19)) via the κ‐O,S‐bidentate mode. The obtained ligands and complexes were spectroscopically and structurally characterized. These Cu(I) products (3‐19) were experimentally used as catalysts for the oxidation of 1‐phenylethanol.

Construction of chiral crown ethers in robust covalent organic frameworks for electrochromatographic enantioseparation

ABSTRACT Capillary electrochromatography (CEC) is a rapidly emerging separation technique that merges the high separation efficiency of capillary electrophoresis with the exceptional selectivity of liquid chromatography. However, it remains a synthetic challenge to design functional chiral stationary phases (CSPs) with high chemical stability against acid and base in CEC enantioseparation. Here we demonstrate that incorporating chiral crown ethers into stable covalent organic frameworks (COFs) enables efficient and stable separations of racemates by CEC. This facilitates the crafting of two three-dimensional (3D) chiral COFs by polycondensation of a chiral 1,1'-binaphyl-20-crown-6-derived dialdehyde and tetraamines with diisopropyl substituents. Both feature an 11-fold interpenetrated diamond framework, characterized by tubular open channels decorated with chiral crown ethers serving as enantioselective recognition and binding sites. These frameworks demonstrate excellent stability in water, acid and base, thanks to the presence of bulky isopropyl groups that shield the dynamic imine linkages. Moreover, the precisely defined COF channels enhanced the accessibility of the enclosed crown ethers to the analytes while providing strong protection against harsh environments, rendering them suitable for CSPs in CEC separations. They can effectively separate some important enantiomers, including ketones, epoxides and alkaline substances, when utilized as coatings on chiral columns, particularly facilitating the chiral separation of drugs. This study advances the application of COFs in electrochromatographic separations, expanding the scope of porous materials design and engineering to create COFs with targeted enantioselective properties.

Alkoxy-Functionalized Hydroxamate/Zinc Metal-Organic Frameworks and the Effects of Substituents and Acid Addition on Their Structures.

Single crystals of alkoxy-functionalized hydroxamate/zinc metal-organic frameworks (MOFs) were obtained by fixating the hydroxamate moiety via intramolecular hydrogen bonding. The resulting MOF structures depend on the steric demand of the alkoxy groups, whereby the incorporation of bulky isopropyl groups affords porous hydroxamate/zinc MOFs. The topological structures of the isopropyl-substituted MOFs could be controlled by adding acid.

Synthesis, characterization and ethylene (Co)polymerization of binuclear Vanadium(IV) catalysts based on xanthene-bridged bis-salicylaldiminato ligands

Bimetallic complexes have attracted much attention due to their excellent catalytic performances in many fields. Herein six xanthene-bridged bis-salicylaldiminato [ON] bidentate binuclear vanadium(IV) complexes V2L1-V2L6 were synthesized and characterized by MALDI-TOF-MS, FTIR spectroscopy and elemental analysis, and the crystal structures of V2L1 and V2L2 were further characterized by XRD, in which each vanadium atom was found coordinated with three O, one Cl and one N atoms to form a twisted trigonal bipyramidal configuration. Under Et2AlCl and ethyl trichloroacetate (ETA) activation, all the binuclear vanadium(IV) complexes exhibited high activity over 106 g/mol(V)·h·atm towards ethylene polymerization and copolymerization with 1-hexene. The activity of binuclear V2L4 for ethylene polymerization was much higher than that of its mononuclear counterpart VL, indicating that strong bimetallic synergetic effect existed in these binuclear vanadium complexes. The substituents on the ligands have a great influence on the catalytic performances of the vanadium complexes. The introduction of bulky isopropyl group into the ligand had little effect on the activity, but the introduction of electron-withdrawing fluorine atoms could significantly increase the activity, suggesting that the electronic, rather than the steric factors had a greater impact. As the amount of fluorine substituent on the iminophenyl moiety of the complex increased, the catalytic activity increased appreciably. With five fluorine atoms on the benzene ring of the imine moiety, the complex V2L6 showed the highest activity of 1.10 × 107 g/mol(V)·h·atm for ethylene polymerization to produce the highest molecular weight of polyethylene. Furthermore, the introduction of fluorine atoms into ligands could also increase the catalytic activity of vanadium complexes, comonomer incorporation and molecular weight of obtained copolymer towards ethylene/1-hexene copolymerization. The highest copolymerization activity of V2L6 was 4.13 × 106 g/molV·h·atm, which was more than three time that of the fluorine-free complex V2L1. The insertion rate of 1-hexene for the fluorine-containing complex V2L3-V2L6 was also higher than that for V2L1.

High−molecular weight poly(2-substituted 1,3-diene)s using iminopyridine iron precatalysts at high polymerization temperature and low iron loading

The synthesis of a series of iron(II) dichloride complexes bearing iminopyridine (ImPy) ligands, differing in the substituents at the pyridine, bridging carbon and N−aryl ring is described (1-LHPh−7-LHS). The X-ray structures of some of them are presented. All the iron compounds and, for comparison, the already reported 8-LHPhP, that features bulky ortho isopropyl N−aryl substituents, have been investigated as precatalysts for the polymerization of 2-substituted 1,3-dienes, i.e., isoprene and β-myrcene, using a low excess of methylaluminoxane (MAO) as alkylating reagent, iron loading as low as 0.025 mol% and variable temperature up to 100 °C. The goal is to have insights into ligand effects on catalyst reactivity and selectivity and to recognize the most robust iron precatalysts to access high-molecular weight (MW) polymers using low iron loading and high polymerization temperature, which meets current demands of mild, operationally simple approach. Particularly, the ketimine 4-LMePh and 5-LPhPh are more stable and least prone to chain termination than all the aldimine parents. 4-LMePh and 5-LPhPh produce cis-1,4/3,4 ultra-high-MW poly(isoprene)s and solid high-MW poly(β-myrcene)s, while maintaining narrow and unimodal molecular weight distribution. In this study we intentionally kept the monomer conversion low to provide a valuable assessment of catalyst stability, uncorrupted by mass or heat transport limitations. Furthermore, the synthesis of the unsubstituted aminopyridine (AmPy) iron(II) dichloride complex 9-LAPh, analogue to 1-LHPh, is described. 9-LAPh has been demonstrated to be a valuable probe for stability studies. Given the variety of catalytic transformations and substrates for which (ImPy)FeCl2 precatalysts have promising reactivity and selectivity, those developed in this study offer promising applications also beyond the polymerization of 1,3-dienes.

Noncovalent Interactions in Crowded Benzene Systems: How Much Strain Is Too Much? Attractions Overcome Repulsions!

AbstractIn molecular design, large alkyl groups are used to introduce bulk and steric crowding of the catalytic center to improve catalytic efficiency and selectivity. The bulky groups are highly polarizable, increasing their ability to participate in stabilizing noncovalent interactions. The rationalization of noncovalent interaction trends is of both fundamental and practical interest as it provides new design concepts for catalysis and synthesis. Highly congested molecules always present challenges to chemists. Crowded benzene systems are an important class of compounds with well-established thermodynamic properties. The latter were used in this work to develop tools to quantify the degree of stabilization or destabilization in benzene systems crowded with bulky isopropyl and tert-butyl substituents. The basic idea was to quantify the delicate balance between repulsive and attractive interactions inherent in crowded benzene systems. The ensemble of experimental thermodynamic data and DFT-D3 calculations enabled the development of quantitative scales of the dispersion contributions and their understanding at the molecular level.

Enantioselective Synthesis of α-Alkenylated γ-Lactam Enabled by Ni-Catalyzed 1,4-Arylcarbamoylation of 1,3-Dienes

Enantioselective Synthesis of α-Alkenylated γ-Lactam Enabled by Ni-Catalyzed 1,4-Arylcarbamoylation of 1,3-Dienes

Conformational Structure, Infrared Spectra and Light-Induced Transformations of Thymol Isolated in Noble Gas Cryomatrices

The conformational space of the natural product thymol (2-isopropyl-5-methylphenol) was investigated using quantum chemical calculations at the B3LYP and MP2 levels, which revealed the existence of four types of conformers differing in the orientation of the isopropyl and hydroxyl groups. Thymol monomers were isolated in noble gas (Ar and Xe) matrices (at 15 K) and characterized by IR spectroscopy. With the support of B3LYP harmonic vibrational calculations, the two most stable trans-OH-conformers, differing in the isopropyl orientation, were identified in the cryomatrices. The two less stable cis-OH conformers were not detected as they shall undergo fast tunneling to the most stable ones. Annealing experiments in a Xe matrix up to 75 K did not lead to any conversion between the two isolated conformers, which is in accordance with the significative energy barrier computed for rotamerization of the bulky isopropyl group (~24 kJ mol−1). Vibrational excitation promoted by broadband or by narrowband irradiation, at the 2ν(OH) frequencies of the isolated conformers, did not lead to any conversion either, which was interpreted in terms of a more efficient energy transfer to the hydroxyl rotamerization (associated with a lower energy barrier and a light H-atom) than to the isopropyl rotamerization coordinate. Broadband UV irradiation experiments (λ > 200 nm) led to a prompt transformation of matrix isolated thymol, with spectroscopic evidence suggesting the formation of isomeric alkyl-substituted cyclohexadienones, Dewar isomers and open-chain conjugated ketenes. The photochemical mechanism interpretation concords with that reported for analogous phenol derivatives.

Green polymer synthesis and low dielectric properties obtained by oxidative polymerization of thymol with CuCl-2-(p-tolyl)pyridine catalyst

Polymerization of thymol (2-isopropyl-5-methylphenol) was conducted using a bulky copper catalyst (CuCl-2-(p-tolyl)pyridine) in toluene under dioxygen atmosphere to give the corresponding 1,4-coupled polythymol (PPETh) with the Mn up to 22.7 kDa in moderate yield. The OH absorption in the IR spectrum disappeared almost completely and the presence of only nine signals in the 13C NMR spectrum clearly indicated the satisfactory formation of the expected linear PPETh. The PPETh exhibited good solubility in tetrahydrofuran, N,N-dimethylformamide, 1,4-dioxane, and CHCl3 (well-known for preparing industrial PPE26 from oxidative polymerization of 2,6-dimethylphenol), and good thermostability (Td5 in N2 of 410 °C). PPETh was mixed with PPE26 and the tough films were successfully prepared by the hot-press method in the weight fraction of PPETh up to 60%. TMA and DMA were performed to evaluate the Tg and the CTE of the films at 179–222 °C and 82–130 ppm/K, respectively. The dielectric properties were measured using a cavity resonator, in which the relative permittivity ranged from 2.28 (PPETh60%) to 2.46 (PPE26), and the dissipation factor from 0.00173 (PPE26) to 0.00495 (PPETh60%) at 10 GHz. The bulky isopropyl substituent gave to the PPETh polymer good solubility and insulating property with maintained thermal stability.

Structure-property relationship of poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes with pendant sterically crowded quaternary ammoniums

Steric hindrance engineering is of great significance to the preparation of new stable organic cations and durable polymeric anion exchange membrane materials. In this work, we presented a study of the structure-property relationship in quaternized poly (2,6-dimethyl-1,4-phenylene oxide) containing bulky n-propyl, isopropyl, or cyclohexyl-functionalized quaternary ammonium moieties. To our surprise, PPO-iP membranes possessing isopropyl-based QA cations showed higher water uptake than n-propyl- and cyclohexyl-containing analogues (PPO-nP and PPO-CH), in which obvious microphase-separated morphology was found. Thus, PPO-iP membranes displayed the highest hydroxide conductivity at 20 °C in water (37.3 mS/cm, IEC = 1.90 mmol/g). A standard protocol (1 M or 2 M NaOH at 60 °C) was used to determine the chemical stability of model cations and membranes both having sterically crowded QAs. Minor loss (<2%) in conductivity was observed for PPO-CH membranes after the treatment in 2 M NaOH at 60 °C for 216 h, highlighting the excellent alkaline stability, while significant degradation of PPO-iP and PPO-nP was confirmed by NMR characterization of the aged samples. In addition, the prepared PPO-based AEMs having sterically crowded QA cations were compared in alkaline H2/O2 fuel cells, demonstrating that the highly conductive PPO-iP membrane exhibited a peak power density of 182 mW/cm2 under optimized testing conditions.

Giant Vesicles of Amphiphilic Diblock Copolymer with Branched Side Chains

Biomolecules of lipids and proteins optimize the hydrophobicity to precisely form their three-dimensional structures. The branching of hydrocarbon chains is appropriate for fine-tuning the hydrophobicity of the molecules because it provides a slight reduction in hydrophobicity. This paper describes the morphological changes of vesicles formed by an amphiphilic diblock copolymer supporting branched side chains in the hydrophobic block to elucidate the steric effect of the side chains on the morphology. The vesicles consisting of poly(methacrylic acid)-<i>block</i>-poly(isopropyl methacrylate-<i>random</i>-methacrylic acid), PMAA-<i>b</i>-P(iPMA-<i>r</i>-MAA), were obtained by the polymerization-induced self-assembly using the photo-nitroxide mediated controlled/living radical polymerization (photo-NMP) in an aqueous methanol solution (methanol/water=3/1 <i>v</i>/<i>v</i>). PMAA-<i>b</i>-P(iPMA-<i>r</i>-MAA) with a very high ratio of the iPMA units produced spherical vesicles. As the iPMA ratio decreased, the vesicles shrank, expanded again, and changed into sheets. The chain length of the hydrophobic block also dominated the morphology. For the high iPMA ratio constant, the copolymers with a short block produced two domains of micron-sized spherical vesicles and unspecific nano-sized particles fused. An increase in the block length changed the nanoparticles into nanospheres, accompanied by an increase in the number of micron-sized spherical vesicles. By further extending the block length, most of the nanospheres grew into micron-sized spherical vesicles. On the other hand, for the low iPMA ratio constant, an increase in the length of the hydrophobic chain changed the unspecific nanoparticles sheets into aggregates with an inverted hexagonal phase reticularly perforated. The PMAA-<i>b</i>-P(<i>n</i>-propyl methacrylate-<i>r</i>-MAA) copolymer produced flexible sheets with a smooth surface without any pores, while PMAA-<i>b</i>-P(methyl methacrylate-<i>r</i>-MAA) provided rods of laminated sheets. It was found that the formation of the inverted hexagonal phase was due to the steric repulsion of the bulky isopropyl groups in the hydrophobic blocks. These findings indicate that the morphology of the vesicles is manipulated not only by the hydrophobicity of the copolymer, but also by the bulkiness of the branched side chain in the hydrophobic block.

Antiproliferative, Antimicrobial and Antiviral Activity of β-Aryl-δ-iodo-γ-lactones, Their Effect on Cellular Oxidative Stress Markers and Biological Membranes.

The aim of this work was the examination of biological activity of three selected racemic cis-β-aryl-δ-iodo-γ-lactones. Tested iodolactones differed in the structure of the aromatic fragment of molecule, bearing isopropyl (1), methyl (2), or no substituent (3) on the para position of the benzene ring. A broad spectrum of biological activity as antimicrobial, antiviral, antitumor, cytotoxic, antioxidant, and hemolytic activity was examined. All iodolactones showed bactericidal activity against Proteus mirabilis, and lactones 1,2 were active against Bacillus cereus. The highest cytotoxic activity towards HeLa and MCF7 cancer cell lines and NHDF normal cell line was found for lactone 1. All assessed lactones significantly disrupted antioxidative/oxidative balance of the NHDF, and the most harmful effect was determined by lactone 1. Contrary to lactone 1, lactones 2 and 3 did not induce the hemolysis of erythrocytes after 48 h of incubation. The differences in activity of iodolactones 1–3 in biological tests may be explained by their different impact on physicochemical properties of membrane as the packing order in the hydrophilic area and fluidity of hydrocarbon chains. This was dependent on the presence and type of alkyl substituent. The highest effect on the membrane organization was observed for lactone 1 due to the presence of bulky isopropyl group on the benzene ring.

Peculiarities of three-component cyclization of ethyl 4,4,4-trifluoroacetoacetate and 1,2-ethanediamines with 3-methylbutan-2-one

The peculiarities of the three-component cyclization of ethyl 4,4,4-trifluoroacetoacetate and 1,2-ethanediamines with 3-methylbutan-2-one into hexahydroimidazo[1,2-a]pyridin-5-ones were studied. The reactions proceeded under mild conditions. The use of methyl ketone with a bulky isopropyl substituent increased the stereoselectivity of the transformations, but the reaction with 1,2-diaminopropane was accompanied by the formation 4-[(1-ammoniopropan-2-yl)amino]-1,1,1-trifluoro-4-oxobut-2-en-2-olate as a by-product.

Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale.

The Cu‐catalyzed reaction of substituted α‐diazoesters with fluoride gives α‐fluoroesters with ee values of up to 95 %, provided that chiral indane‐derived bis(oxazoline) ligands are used that carry bulky benzyl substituents at the bridge and moderately bulky isopropyl groups on their core. The apparently homogeneous solution of CsF in C6F6/hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH2Cl2/HFIP also provides good results. DFT studies suggest that fluoride initially attacks the Cu‐ rather than the C‐atom of the transient donor/acceptor carbene intermediate. This unusual step is followed by 1,2‐fluoride shift; for this migratory insertion to occur, the carbene must rotate about the Cu−C bond to ensure orbital overlap. The directionality of this rotatory movement within the C 2‐symmetric binding site determines the sense of induction. This model is in excellent accord with the absolute configuration of the resulting product as determined by X‐ray diffraction using single crystals of this a priori wax‐like material grown by capillary crystallization.

Exploring the Utility of Buchwald Ligands for C-H Oxidative Direct Arylation Polymerizations.

Oxidative C-H/C-H cross-coupling polymerizations provide an opportunity to synthesize conjugated polymers with an increased ease of monomer preparation, reduced environmental impact, and increased sustainability. Considering these attributes, it is necessary to expand the diversity of monomers that readily and efficiently participate in this coupling strategy to enable the development of conjugated polymers with a wide range of properties. Herein, the oxidative direct arylation polymerization toolbox is expanded to include 3,4-propylenedioxythiophene being synthesized via C-H/C-H cross-coupling methodologies. In conjunction with these efforts, the utilization of Buchwald ligands in C-H/C-H cross coupling polymerizations also is reported, and variations in the ligand structure provide insight into the role ligand choice has on C-H cross-coupling polymerizations. Specifically, it is determined that the phosphine functionality affects the rate-determining, concerted metalation-deprotonation step of the catalytic cycle, while bulky isopropyl substituents on the ligand's lower aryl ring promote reductive elimination. By balancing these steric effects on the ancillary ligands, polymers are synthesized to exhibit molecular weights above the effective conjugation length, with recovered yields >90%. In addition to expanding the scope of conjugated polymers accessible via oxidative direct arylation polymerization, these results provide the foundational understanding for utilizing Buchwald-type ligands in C-H-activated polymerizations.

Preparation of Half- and Post-Metallocene Hafnium Complexes with Tetrahydroquinoline and Tetrahydrophenanthroline Frameworks for Olefin Polymerization.

Hafnium complexes have drawn attention for their application as post-metallocene catalysts with unique performance in olefin polymerization. In this work, a series of half-metallocene HfMe2 complexes, bearing a tetrahydroquinoline framework, as well as a series of [Namido,N,Caryl]HfMe2-type post-metallocene complexes, bearing a tetrahydrophenanthroline framework, were prepared; the structures of the prepared Hf complexes were unambiguously confirmed by X-ray crystallography. When the prepared complexes were reacted with anhydrous [(C18H37)2N(H)Me]+[B(C6F5)4]−, desired ion-pair complexes, in which (C18H37)2NMe coordinated to the Hf center, were cleanly afforded. The activated complexes generated from the half-metallocene complexes were inactive for the copolymerization of ethylene/propylene, while those generated from post-metallocene complexes were active. Complex bearing bulky isopropyl substituents (12) exhibited the highest activity. However, the activity was approximately half that of the prototype pyridylamido-Hf Dow catalyst. The comonomer incorporation capability was also inferior to that of the pyridylamido-Hf Dow catalyst. However, 12 performed well in the coordinative chain transfer polymerization performed in the presence of (octyl)2Zn, converting all the fed (octyl)2Zn to (polyolefinyl)2Zn with controlled lengths of the polyolefinyl chain.

Enhanced Separation Concept (ESC): Removing the Functional Subunit from the Electrode by Molecular Design

A new concept to improve the reliability of functional single molecule junctions is presented using the E‐field triggered switching of FeIIbis‐terpyridine complexes in a mechanically controlled break junction experiment as model system. The complexes comprise a push‐pull ligand sensing the applied E‐field and the resulting distortion of the FeII ligand field is expected to trigger a spin‐crossover event reflected in a sudden jump of the transport current. By molecular engineering, the active centre of the complex is separated from the gold electrodes in order to eliminate undesired side‐effects. Two aspects are considered to isolate the central metal ion, namely the spacing by introducing additional alkynes, and the steric shielding achieved by bulky isopropyl groups. With this small series of model complexes, a pronounced correlation is observed between the occurrence of bistable junctions and the extent of separation of the central metal ion, affirming the hypothesized Enhanced Separation Concept (ESC).

Precise control of single unit monomer radical addition with a bulky tertiary methacrylate monomer toward sequence-defined oligo- or poly(methacrylate)s via the iterative process

Iterative single unit monomer radical addition with a bulky tertiary methacrylate monomer, adamantyl and isopropyl pendant methacrylate (IPAMA), under ATRP conditions was studied in detail toward the syntheses of sequence-defined oligo- or poly(methacrylate)s in higher yields.

Synthesis of ultra‐high‐molecular‐weight ethylene‐propylene copolymer via quasi‐living copolymerization with N‐heterocyclic carbene ligated vanadium complexes

ABSTRACTThe quasi‐living copolymerization of ethylene with propylene was achieved by using N‐heterocyclic carbene (NHC) ligated vanadium complex (V3, VOCl3[1,3‐(2,6‐iPr2C6H3)2(NCH)2C:]) due to the stabilization of active center by the introduction of bulky and electron rich NHC ligand with bulky isopropyl substituents at the ortho positions of the phenyl rings. The weight‐average molecular weight (Mw) of the resulting copolymer increases linearly with its weight in 20 min. The ultra‐high‐molecular‐weight (UHMW) ethylene‐propylene copolymer (Mw = 1612 kg mol−1) can be synthesized with V3/Et3Al2Cl3 catalytic system. The novel complex V4′ (VCl3[1,3‐(2,4,6‐Me3C6H2)2(NCH)2C:]·2THF) was constructed by the introduction of two coordinated tetrahydrofuran molecules and decrease in steric hindrance at the ortho positions of phenyl rings. The UHMW ethylene‐propylene copolymer (Mw = 1167 kg mol−1) can also be synthesized by using V4′/Et3Al2Cl3 catalytic system. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 553–561

Modulating stability of functionalized fullerene cations [R-C60 ]+ with the nature of R-group.

In this study, the first comprehensive theoretical investigation of the stability of functionalized fullerene-based cations [R-C60 ]+ and its relationship with the nature of the attached R-group was performed. C60 -Fullerene core was functionalized with an alkyl group of different length (R = (CH2 )n CH3 , where n = 0-9). This set was further complemented by bulky isopropyl and tert-butyl and conjugated phenyl groups. A detailed study of the relative stability of target cationic species was accompanied by in-depth investigation of their electronic structure and aromaticity using a large set of descriptors of different nature. The stability of target species was considered with respect to two alternative and competing mechanisms of bond breaking, namely, heterolytic ([R-C60 ]+ → R+ + C60 ) and homolytic ([R-C60 ]+ → R• + C60 +• ) ones. The transformation of strained sp2 -carbon atom in unperturbed C60 -fullerene to nonconstrained tetrahedral sp3 -type in functionalized derivatives was found to be the driving force for the formation of its functionalized cations. In spite of the fact that all systems under consideration were found to be corresponding to local minima on corresponding potential energy surfaces, the functionalization of C60 -core with the smallest and simplest methyl group resulted in most stable compound, as evaluated by bonding energy between R+ and fullerene fragment (in the light of both mechanisms). Subsequent elongation of the alkyl chain or introducing bulky groups led to notable decrease of the bonding energy and, as consequence, of the stability within the framework of heterolytic bond cleavage, whereas homolytic pathway assumes opposite-slight increase of stability along with lengthening of the R-group. The orbital interaction (ΔEorb ) was identified as the main driving force for these trends. In general, the homolytic path was found to be dominating for small-length R-groups such as those with n = 0 and 1. At n = 2, heterolytic and homolytic pathways are equally probable (the difference in corresponding bonding energies is about 1 kcal/mol). However, when the alkyl chain becomes longer (n = 3-9), the cationic bond cleavage appears as the most energetically favorable. © 2018 Wiley Periodicals, Inc.