Amides molecular complexity

Consider a nucleus that can partition between two magnetically nonequivalent sites. Examples would be protons or carbon atoms involved in cis-trans isomerization, rotation about the carbon—nitrogen atom in amides, proton exchange between solute and solvent or between two conjugate acid-base pairs, or molecular complex formation. In the NMR context the nucleus is said to undergo chemical exchange between the sites. Chemical exchange is a relaxation mechanism, because it is a means by which the nucleus in one site (state) is enabled to leave that state. 

Kagan and coworkers determined and studied in detail the crystal structure of a 1 1 molecular complex between (i )-methyl p-tolyl sulfoxide (10) and S)-N-(3,5-dinitrobenzoyl)-l-phenylethylamine (11). They suggested that amide 11, which had been used as a chiral solvating agent for sulfoxides, might find use as a resolving agent for these compounds. ... 

The anions of primary nitramines, like other nucleophiles, can undergo Michael 1,4-addition reactions with a range of a,-unsaturated substrates to form secondary nitramines of varying molecular complexity (Equation 5.18). Kissinger and Schwartz prepared a number of secondary nitramines from the condensation of primary nitramines with a,/3-unsaturated ketones, esters, amides and cyanides. In a standard experiment a solution of the primary nitramine and... 

A method of diversity-oriented synthesis consists in sequencing multicomponent reactions with subsequent transformations that further increase molecular complexity. Thus, amides 223a and b (Scheme 53, both obtained... 

As one would expect, there is a strong correlation between solubility in non-polar solvents, volatility and molecular complexity of metal amide compounds. The degree of association can typically be related to empirical formula (ML ), metal covalent radius and the steric demand of the amide substituents. 

Although, at that time, the term supramolecular chemistry had not yet been coined, the practical potential for inclusion complexation for acetylene alcohol guests 1 and 2 was recognized back in 1968 [12], Spectroscopic studies showed that 1 and 2 formed molecular complexes with numerous hydrogen-bond donors and acceptors, i.e. ketones, aldehydes, esters, ethers, amides, amines nitriles, sulfoxides and sulfides. Additionally, 1 formed 1 1 complexes with several n-donors, such as derivatives of cyclohexene, phenylacetylene, benzene, toluene, etc. The complexation process investigated by IR spectrometry revealed the presence of OH absorption bands at lower frequencies than those for uncomplexed 1 and 2 [12], These data, followed by X-ray studies, confirmed that the formation of intermolecular hydrogen bonds is the driving force for the creation of complexes [13],... 

The primary amides of the group 2 elements, M(NH2)2, are nonmolecular species. " When the NH2 ligand is replaced by the bulky bis(trimethylsilyl)amido group, however, molecular complexes are formed. A complete set of structures has been obtained for Be through Ba (Table 11). The barium bis(trimethylsilyl)amides form a progression of compounds that illustrate the important relationship between ligand bulk and metal nuclearity. The base-free compound, [Ba N(SiMe3)2 ]2, exists as a dimer that can accommodate... 

Figure 2 Sketches and molecular structures of (a) aluminum amid-rnate complex Al HC(CMeNDipp)2 (H atoms removed for clarity) and (b) germanium aminotroponiminate cation [Ge(C7H5N2J-Pr2)]+...

Sometimes smaller porphyrin assemblies could be reversibly dissolved via molecular complex formation. The protoporphyrin-bis-amide 17 with two w-phenylboronic substituents dissolves in 1 30 DMSO/water mixtures, but is heavily aggregated in this medium. The Soret band s intensity was only the half of that in pure DMSO solution and the fluorescence was almost nil. However, upon addition of 10 M fructose the carbohydrate was bound as a molecular complex and the porphyrin became more water-soluble whereby the fluo-recence increased drastically. Other monosaccharides had lesser effects. 

In a follow up report from Schafer s group [52a] in 2012, largely focused on studying the viscoelastic behavior of the polymer, a modified tris(amidate) yttrium complex was used to initiate ROP of e-caprolactone. This slightly bulkier complex with a diisopro-pylphenyl on the nitrogen instead of dimethylphenyl, gave lower molecular weight polymers of just under 1 x lO g/mol, but of a narrower polydispersity index (PDI) of around 1.5 compared with the values of between 2 and 2.5 achieved in previous studies. 

Carlson, R.L. and Drago, R.S. (1963) Thermodynamic data for the formation of molecular complexes between phenyl-substituted amides and iodine. J. Am. Chem. Soc., 85,505-508. 

Tsubomura, H. and Lang, R.R (1961) Molecular complexes and their spectra. XIII. Complexes of iodine with amides, diethyl sulfide, and diethyl disulfide. J. Am. Chem. Soc., 83,2085-2092. 

Caprolactam is an amide and, therefore, undergoes the reactions of this class of compounds. It can be hydrolyzed, Ai-alkylated, O-alkylated, nitrosated, halogenated, and subjected to many other reactions (3). Caprolactam is readily converted to high molecular weight, linear nylon-6 polymers. Through a complex series of reactions, caprolactam can be converted to the biologically and nutritionally essential amino acid L-lysine (10) (see Amino acids). 

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