A combinatorial approach to studying the effects of N-alkyl groups on poly(N-alkyl and N,N-dialkylacrylamide) solubility

Soluble polymers including poly(N-alkylacrylamide)s with low mole percent loadings of pendant groups are of interest in applications in catalysis, synthesis, sequestration, and soluble affinity chromatography where their thermal and phase-dependent solubility facilitates purification and separation. This work describes a library synthesis and study of the effects of polymer composition on the phase-selective solubility of dye-labeled poly(N-n-octadecylacrylamide-co-N-n-butylacrylamide) copolymers. To study the relative importance of n-octadecyl versus n-butyl groups, copolymers with different ratios of n-octadecylacrylamide and n-butylacrylamide but with similar degrees of polymerization and polydispersity were prepared by a split-pool synthesis using a highly soluble poly(N-acryloxy-2-dodecylsuccinimide) as the precursor. Polymer sequestrants were used to remove excess amines and the byproduct N-hydroxyl-2-dodecylsuccinimide without fractionation of the polyacrylamides. Other studies of dye-labeled poly(N,N-dialkylacrylamide)s prepared by the polymerization of N,N-dialkylacrylamides with methyl, ethyl, propyl, butyl, pentyl, and hexyl N-alkyl groups in a variety of thermomorphic or latent biphasic polar/nonpolar solvent mixtures showed that poly(N,N-dialkylacrylamide)s like poly(N-alkylacrylamide)s have phase-selective solubility that is highly dependent on the size of the N-alkyl group.     

Photochemical reactions of N-alkyl and N,N-dialkylimidazolidinetriones

N-Akyl and N,N-Dialkylimidazolidinetriones undergo intramolecular hydrogen abstraction on irradiation to give elimination, intramolecular disproportionation, and cyclization products.     

Unusual temperature effects on the non-equivalence of geminal methyl groups

The geminal anisochronism (Δδ) of the isopropyl methyl groups in the ¹H n.m.r. spectrum of N-[2-methyl-1-(1-naphthyl)propylidene]benzylamine showed unusually pronounced temperature and solvent effects. It is noteworthy that both accidental and dynamic equivalences were encountered. Slow rotation around the naphthyl–imino bond is responsible for the diastereotopic nature of the geminal methyl groups, and possible reasons for the temperature and solvent effects are considered. Surprisingly, the temperature effect was not reflected in the ¹³C anisochronism of the methyl carbon nuclei. These observations underline the need for caution in drawing firm conclusions from variable temperature studies on geminal non-equivalence.     

Complexation of N-alkyl(aryl)- and N,N-dialkylcarbamoylmethylphosphine oxides with the f-elements

Complexation of N-alkyl(aryl)carbamoylmethylphosphine oxides (CMPO) and their N, N-dialkyl analogs in neutral media was studied. N-Alkyl derivatives react with praseodymium and europium nitrates both in solution and in the individual state to give 1: 2 and 1: 3 complexes, depending on the ratio of the starting reagents; for N-aryl amides, 1: 3 complexes were obtained only. With the uranyl cation, both N-alkyl and N,N-dialkyl derivatives of CMPO form various 1: 1 complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1862, September, 2008.     

ESR spectra of N-alkyl N′,N′-dimethylcarbamoyl and N-tert-butyl N-carbobenzyloxy aminyl radicals

The first ESR spectral data for the title amidyl radicals are reported. They are consistent with π electronic ground states.     

On the conformation of ethyl groups in diethylsilane molecules

Conformations of the model dichlorodiethylsilane molecule were systematically studied in order to establish conformations of the alkyl groups relative to the Si—C bond in polydialkyl-silanes. The temperature dependence of the Raman and IR spectra was studied. Quantum chemical calculations were performed of the energy characteristics as well as the normal mode frequencies, eigenvectors, and intensities of four possible conformers. In the crystalline state Et₂SiCl₂ exists as the most energetically favorable aa-conformer, whereas in the liquid state Et₂SiCl₂ represents a mixture of almost isoenergetic g₊g₊-and ag-conformers with the predomination of the latter at room temperature.     

Intramolecular orbital interactions in and conformation of N,N′-diphenylcarbodiimide studied by photoelectron spectroscopy

The intramolecular orbital interactions in N,N′-diphenylcarbodiimide were revealed by photoelectron spectroscopy and the phenyl rings in this compound were found to be twisted by ca. 25° from the perpendicular model.     

Adsorption and aggregation properties of amino acid-based N-alkyl cysteine monomeric and N,N'-dialkyl cystine gemini surfactants

An amino acid-based gemini surfactant derived from cystine (2CnCys, where n represents the hydrocarbon chain lengths of 8, 10, and 12) was synthesized by reacting cystine with n-alkyl bromide, and its adsorption and aggregation properties were characterized by measurements of equilibrium and dynamic surface tension and dynamic light scattering. The properties of 2CnCys were compared with those of an amino acid-based monomeric surfactant derived from cysteine (CnCys). For n=8 and 10, when compared to CnCys, 2CnCys exhibited excellent surface activities, such as a lower critical micelle concentration (cmc), greater efficiency in lowering the surface tension of water, and smaller area occupied per molecule. Adsorption rate at air/water interface decreased with an increase in hydrocarbon chain length, chain number, and concentration of respective compounds. Further, the kinetics were discussed using the monomer diffusion coefficient obtained from short and long time scales in dynamic surface tension plots. In addition, the aggregation properties of 2CnCys for n=8 and 10 differed from those in the case of n=12. In other words, relatively larger micelles with diameters of approximately 7 nm were formed by 2CnCys for n=8 and 10 in comparison to those formed by CnCys (2-3 nm). On the other hand, for a 0.832 mmol dm-3 2C12Cys solution, the aggregation structure investigated by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) revealed the coexistence of small unilamellar vesicles and small rods.     

New aromatic-aliphatic polyesters based on N-alkyl carbazole groups in the main chain. Synthesis-structure-properties relationships

Polyesters based on N-butyl or N-octylcarbazole units in the main chain were synthesized either by direct polycondensation between the carbazole dicarboxylic acids and ethylene glycol or from alcoholysis of the 2-hydroxyethyl diesters in the presence of different catalytic systems. Depending on the reaction conditions together with the nature and the concentration of the catalyst, diethylene glycol (DEG) is formed as a side-reaction product. DEG is incorporated in the polyester chain concurrently with EG and leads to the formation of ether links in the spacers. The DEG content as well as the length of the alkyl pendant group of the carbazole unit were found to have a drastical effect on the thermal properties. Furthermore, these materials form charge transfer complexes through carbazole nuclei with electron acceptor and electron donor molecules as well.     

Organoaluminium and -gallium compounds with N,N-diisopropylaminomethyl groups

The N,N-diisopropylaminomethyl aluminium compound [tBu2AlCH2NiPr2 x LiCl]2(1) and the gallium compounds Li[tBu2Ga(CH2NiPr2)2](2) and [tBu2GaCH2N(H)iPr2]Cl x tBu3Ga (3) were prepared by transmetallation of N,N-diisopropylaminomethyllithium LiCH2NiPr2 with di-tert-butylaluminium or -gallium chloride, and characterised by elemental analyses, multinuclear NMR spectroscopy (1H, 13C, 27Al, 7Li) and IR spectroscopy. The crystal structures have been determined by single crystal X-ray diffraction. Compound aggregates as a centrosymmetric dimer, with two Al-C-N units connected by a frame of two LiCl molecules [Al-Cl 2.367(1), Cl-Li 2.339(4) and 2.374(4), Li-N 1.977(4)A]. Compound 2 is a lithium organogallate with two weak LiN bonds [1.965(7) and 1.937(7)A]. Compound 3 contains two different moieties: tBu3Ga and a [tBu2GaCH2N(H)iPr2]+ cation, which are bridged by a Cl- anion [Ga-Cl 2.445(1) and 2.579(1), HCl 2.362(3)A].     

Further evidence of the intrinsic chemical shift non-equivalence

The influence of hydrogen bonds on the chemical shift non-equivalence of geminal methyl groups in recently investigated carbinols has been eliminated by using the formyl derivatives of the general formula RCH(OCHO)C(NO₂)Me₂. The observed increasing non-equivalence, with the rise of temperature, provides more convincing evidence of the intrinsic non-equivalence.     

Electrical properties,vibrational spectra,and conformation of N,N-di (chloromethyl)amides

Conclusions N,N-Di(chloromethyl)amides have a conformation of the gg type with dihedral CNCCl angles of 100–120°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2801–2805, December, 1982.     

Hindered rotation of the dimethylamino and dimethylthioamide groups in two ortho substituted N,N-dimethylthiobenzamides

Hindered rotation in two o-substituted N,N-dimethylthiobenzamides was investigated by variable temperature ¹H NMR spectroscopy. For one compound, the enthalpies and entropies of activation for (i) thioamide group rotation around the Ar? C bond and (ii) dimethylamino group rotation around the C? N bond were obtained by full line shape analysis; a possible coupling between the two processes is discussed. A new simple method has also been applied to the analysis of dimethylamino exchange and results are in complete agreement with the full line shape analysis with somewhat better precision.