Formamidine dimer

A study investigating the influence of the stacking <7- tt and tt- tt interactions on the shielding tensors has also been discussed recently. However, only the model systems of benzene and formamidine dimers were investigated. ... 

Sponer, J. and Hobza, P. (2000) Interaction energies of hydrogen-bonded formamide dimer, formamidine dimer, and selected DNA base pairs obtained with large basis sets of atomic orbitals, J. Phys. Chem. A 104, 4592-4597. 

Figure 29.7 Stationary points representing the reactant (R), transition state (TS), product (P), and (where applicable) intermediate (Int) related to double proton transfer in analogs of the formic acid dimer (a) formamidine dimer [43] ...

The MCSCF method has been used to calculate the intermolecular spin-spin coupling constants in formamide-formamide and formamide-formamidine dimers, modelling the hydrogen bond in peptides and adenine-tymine (or adenine-uracil) pair in a nucleic acid, respectively. The obtained hydrogen-bond-transmitted coupling constants are visualized in Fig-... 

Fig. 1. The hydrogen-bond-transmitted coupling constants calculated at the MCSCF level for formamide-formamide and formamide-formamidine dimers Asterix denotes the numbers for which SD terms are omitted.

Dynamics in the solid state include processes of an intramolecular proton transfer the tautomerism of porphyrin [10] or the intramolecular proton transfer in cyclic AW-bisaryl formamidine dimers [11] was studied by means of CP MAS NMR. 

Meschede, L., Limbach, H-H. (1991). Dynamic NMR Study of the Kinetic HH/HD/DD Isotope Effects on the Double Proton Transfer in Cyclic Bis(p>-fluorophenyl)formamidine Dimers. J. Phys. Chem., VoL95, p>p. 10267-10280 Michaelis, L. Menten, M.L., (1913). Die Kinetik der Invertinwirkung. Biochemisches Zeitschrift, Vol. 49, pp. 333-369. 

Based on PES calculations on the isolated complexes, the existence of further cyclic ion pairs has been suggested, among them for ammonium salts of zeolite-clusters or ammonium tetrafluoroborate (Ref.46, 3-21G and 6-3IG ab initio basis sets). In these cases, an asymmetric hydrogen bonded form did not occur as a second minimum on the PES. Surprisingly, the proton transfer in the eight-membered formamidine dimer is supposed to pass a transition structure of lower symmetry to form an ion-pair like intermediate... 

Dynamic NMR study of kinetic HH/HD/DD isotope effects of double proton transfer in cyclic bis(p -fluorophenyl)formamidine dimers. /. Phys. Chem., 95,... 

ET-IR spectroscopy was employed to investigate the structures of the 1 1 complexes between Li" and the guanidine-substituted azo compounds pyiidine-2-azo-p-phenyltetramethylguanidine and 4,4 -bis(tetramethylguanidine)azoben-zene. Both Li" complexes exist as dimers in acetonitrile solution.The structural chemistry of potassium N,N -di(tolyl)formamidinate complexes has been investigated in detail. These compounds were prepared by deprotonation of the parent Af,N -di(tolyl)formamidines with potassium hydride (Scheme 13). The resulting adducts with either THE or DME display one-dimensional polymeric solid-state structures that exhibit /r-fj fj -coordinated formamidinates. 

The role of steric influences on the formation of various vanadium amidinate complexes in the oxidation states +2 and +3 has been studied in detail. The reaction of VCl2(TMEDA)2 and of VCl3(THF)3 with 2 equivalents of formamidinate salts afforded dimeric V2[HC(NCy)2l4 (cf. Section IV.E) with a very short V-V multiple bond and [ [HC(NCy)2 V(/i-Cl)l2 which is also dimeric (Scheme 107). The formation of V2[HC(NCy)2l4 was shown to proceed through the intermediate monomeric [HC(NCy)2l2V(TMEDA), which was isolated and fully characterized. The dinuclear structure was reversibly cleaved by treatment with pyridine forming the monomeric [HC(NCy)2l2V(py)2. ... 

Because silylation with HMDS 2/TCS 14 in acetonitrile at ambient temperature converts the unreactive a-chloroketone moiety of 743 into an /Z-mixture of reactive alkyl 4-chloro-3-trimethylsilyloxycrotonates 746a, b [230, 231] which can be isolated and distilled, if humidity is excluded, silylation of 743a, b in the presence of ami dine salts such as 745 gives the desired ethyl or methyl imidazole(4,5)-acetates 748a, b via IMz and 747b. The reaction of formamidine acetate with 746a,b affords 745 (with R=H) in up to 70% yield [232, 233] (Scheme 5.79). As side reactions one must, e.g., take into account the reaction of 746 with ammonia to give 755 which subsequently dimerizes to the pyrazine 756, as discussed in Section 5.5.3. 

Precursors based on Mo2" + and Rh2" + cores have been used in combination with dicarboxylate linkers to construct supramolecular arrays. Dimer-of-dimers, trimer-of-dimers (molecular triangles), and tetramer-of-dimers (molecular squares) have been prepared using this approach. Judicious selection of precursors and linkers are essential for the successful synthesis of the desired molecular architectures. A total of twelve dimer-of-dimers (100-111) of general formula [(DAniF)3M02]O2C-X-CO2M02[(DAniF)3] (DAniF = A,A -di(/ -anisyl)formamidinate) have been synthesized in which two M02 units are connected by bridging dicarboxylates. These compounds were prepared in one-pot reactions (Scheme 27). It is important to note that the six equatorial positions of the precursors are blocked in order to... 

Carboxylate-bridged Cr dimers are synthesized from chromocene. Benzoic acid, pivalic acid, and 9-anthracenecarboxylic acid react with (f/ -CsH5)2Cr to form Cr2(02CR)4 dimers. Chromium hexacarbonyl is oxidized to dimeric Cr(II) complexes by 2,4-dimethyl-6-hydroxypyrimidine and A, A -(3,5-xylyl) formamidine in refluxing... 

Figure 6.10 The two tautomer forms of a carboxylic acid dimer (upper drawing) and of formamidine H-bonded to two HjO molecules (bottom). One passes from one form to the other one by H-atom transfers.

The other dimers in Fig. 29.7 show asymmetry. If the proton transfer potential is asymmetric, there will be no synchronous transfer and at most accidental level splittings. In the formamide dimer [44] the two hydrogen bonds are the same but the donor and acceptor groups are different. The available calculations indicate that the structure of the equilibrium configuration is intermediate between the equilibrium configurations of dimeric formic acid and dimeric formamidine, as... 

The mechanism and sequential steps of the overall reaction were presumed to occur by the base-catalyzed oligomerization of HCN, first to a dimer, and then to a trimer (amino-malonodinitrile) followed by the condensation of this trimer with formamidine to 4-aminoimidazole-5-carbonitrile (AICN) or the corresponding amidine (AICAI). The eyclization into adenine is completed by condensation of either AICN or AICAI with formamidine. Guanine and xanthine are formed by condensation of AICA with urea. ... 

Hydroxyl radicals, generated radiolytically in N2O, react with thiourea and tetram-ethylthiourea to afford a radical cation. Initially an adduct forms between thiourea (or tetramethylthiourea) and HO this is followed by loss of HO and reaction of the resulting monomeric radical cation with a molecule of thiourea (or tetramethylthiourea) affords the dimeric radical cation. In the bimolecular decay of the dimeric radical cation formamidine (or tetramethylformamidine) disulfide is formed. In basic solutions of thiourea (but not tetramethylthiourea), the formation of a dimeric radical anion, via neutralization of the dimeric radical cation and subsequent deprotonation of the neutral dimeric radical, is observed. The reactions of the dimeric radical cation with O2, superoxide radical, phenolate ion, and azide ion have also been studied. ... 

A rare example of [3+3] retrosynthetic disconnection of fluorinated pyrazine ring was implemented by dimerization of fluorinated formamidine 1099 (Scheme 234) [670], Another example is dimerization of azirine derivative 1101 [671],... 

Parra RD (2012) Dimers and trimers of formamidine and its mono-halogenated analogues HN=CHNHX, (X=H, Cl, Br, or I) a comparative study of resonance-assisted hydrogen and halogen bonds. Comput Theor Chem 998 183-192... 

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