NOEs, intramolecular

Note that for 4.42, in which no intramolecular base catalysis is possible, the elimination side reaction is not observed. This result supports the mechanism suggested in Scheme 4.13. Moreover, at pH 2, where both amine groups of 4.44 are protonated, UV-vis measurements indicate that the elimination reaction is significantly retarded as compared to neutral conditions, where protonation is less extensive. Interestingy, addition of copper(II)nitrate also suppresses the elimination reaction to a significant extent. Unfortunately, elimination is still faster than the Diels-Alder reaction on the internal double bond of 4.44. 

Streptokinase has a molecular weight of about 47,000 with a single chain of 415 amino acids there are no intramolecular disulfide bonds (64). The complete nucleotide sequence of the gene encoding the RNA for this protein has been reported (65,66). 

Hydroxymethylmethyldiazirine (209 unprotonated) formed propionaldehyde as the sole product by thermal nitrogen extrusion 4-hydroxy-l,2-diazaspiro[2.5]oct-l-ene (218) formed a mixture of cyclohexanone (73%), cyclohexenol (21%) and cyclohexene oxide (5%). Thermal decomposition of difluorodiazirine (219) was investigated intensively. In this case there is no intramolecular stabilization possible. On heating for three hours to 165-180 °C hexafluorocyclopropane and tetrafluoroethylene were formed together with perfluorofor-maldazine 64JHC59). 

Diazenes of the type REN=C(R )N=NC(R )=NER have a rich structural chemistry. The selenium derivatives 15.11a,b display a cis,trans,cis conformation with two short l,5-Se N contacts (2.65 A). Several sulfur analogues, e.g., 15.1c, have the same structure, but a different cis,trans,cis conformer 15.12 with two 1,4-S N contacts (2.83 A) has also been characterized. A third type of diazene is the trans,trans,trans isomer 15.13a,b with no intramolecular short contacts. ... 

Assuming that no intramolecular or side reactions take place and that all groups are equireactive, the polydispersity index, 7P, of hyperbranched polymers obtained by step-growth polymerization of ABX monomers is given by Eq. (2.2), where pA is die conversion in A groups.196 Note that the classical Flory relationship DPn = 1/(1 — pa) holds for ABX monomer polymerizations ... 

In considering step polymerisation with polyfunctional molecules a number of assumptions are made. They are (i) that all functional groups are equally reactive, (ii) that reactivity is independent of molar mass or solution viscosity, and (iii) that all reactions occur between functional groups on different molecules, i.e. there are no intramolecular reactions. It is found experimentally that these assumptions are not completely valid and tend to lead to an underestimate of the extent of reaction required to bring about gelation. 

In molecules with both an acidic and a basic function, there is in principle the possibility of an intramolecular proton transfer leading to betaines (see above). Due to the values of the functional groups, pyridine and carboxylic acid, in [66] no intramolecular proton transfer takes place and no betaine is formed. 

Although the reaction mechanism of this type of reactions is not fully elucidated, it is easily anticipated that no intramolecular special stabilization effect for the carbanion generated from decarboxylation is expected, different from the case of malonic acid-type compounds. Moreover, cinnamic acid derivatives that have both the electron-donating and withdrawing substituents have been reported to undergo this reaction. This fact suggests that the enzyme itself stabilizes the transition state without the aid of mesomeric and inductive effects of the other part of the substrate molecule itself. If such unknown mechanism also works for other... 

Reference to the infinite structures as networks would seem inconsistent with our assumption, introduced as an approximation, that no intramolecular reactions occur. A randomly branched structure devoid of intramolecular linkages could hardly be called a network the latter term conveys the notion of circuitous interconnections within the structure. Actually, as will appear later, the assumption referred to need only be applied to the finite molecular species its extension to the infinite structure is superfluous. Certainly it will contain an abundance of intramolecular connections, which, in fact, is an essential feature of the gel structure... 

The quantity of primary interest in our thermodynamic construction is the partial molar Gibbs free energy or chemical potential of the solute in solution. This chemical potential reflects the conformational degrees of freedom of the solute and the solution conditions (temperature, pressure, and solvent composition) and provides the driving force for solute conformational transitions in solution. For a simple solute with no internal structure (i.e., no intramolecular degrees of freedom), this chemical potential can be expressed as... 

If there were no intramolecular interactions (such as bonding or excluded volume), then V(R) = 0, and the next guess for the density profile can be obtained directly from Eq. (75). The presence of V(R) necessitates either a multidimensional integration or (more conveniently) a single-chain simulation. 

The observation that XmT of (bpym, Se) is temperature-independent between 50 and 110 K and that no maximum in the susceptibility occurs at temperatures below 50 K suggests that no intramolecular antiferromagnetic coupling in pairs remains in this temperature regime. In fact the magnetisation curves [9] of (bpym, S) and (bpym, Se) at 1.9 K clearly indicate the different nature of the spin pairs involved in each compound in the ground state (Fig. 8). 

The enthalpies of phase transition, such as fusion (Aa,s/f), vaporization (AvapH), sublimation (Asut,//), and solution (As n//), are usually regarded as thermophysical properties, because they referto processes where no intramolecular bonds are cleaved or formed. As such, a detailed discussion of the experimental methods (or the estimation procedures) to determine them is outside the scope of the present book. Nevertheless, some of the techniques addressed in part II can be used for that purpose. For instance, differential scanning calorimetry is often applied to measure A us// and, less frequently, AmpH and AsubH. Many of the reported Asu, // data have been determined with Calvet microcalorimeters (see chapter 9) and from vapor pressure against temperature data obtained with Knudsen cells [35-38]. Reaction-solution calorimetry is the main source of AsinH values. All these auxiliary values are very important because they are frequently required to calculate gas-phase reaction enthalpies and to derive information on the strengths of chemical bonds (see chapter 5)—one of the main goals of molecular energetics. It is thus appropriate to make a brief review of the subject in this introduction. 

The comparisons we will make within each family involve experimental enthalpies of formation and the derived enthalpy of destabilization (DSE). If there are no intramolecular interactions in the nitrosubstituted parent compound, equation 58 would be thermoneutral. 

This approach is admissible because SCSs are well known to be additive unless (i) the conformational equilibrium of the molecule is altered by progressive substitution, and/or (ii) there is no intramolecular substituent interaction whatsoever. Thus, if application of eq. [18] to a rigid molecular system affords ICS values other than zero, such an interaction must exist. In earlier publications (216,221) the abbreviation NAE (nonadditivity effect)—a merely descriptive term—was employed. 

Phase-transfer catalysis has been used to aid the synthesis of sterically hindered a-aminocarboxamides [18] (Table 5.3). No intramolecular cyclization of the sterically... 

Cephalosporins Ester or lactone at the C(4) carboxy group /3-Lactam carbonyl C-atom more electrophilic, no intramolecular acylamido participation Increased up to 130-fold ... 

This structure gives stability to the layers. The fourth, non-bonding pair of electrons is delocalized and free to move within the layers. This gives graphite the ability to conduct an electric current. There are no intramolecular forces between the layers. Dispersion forces attract one layer to another, enabling layers to slide by one another. Graphite feels slippery as a result of this characteristic. In fact, many industrial processes use graphite as a lubricant. 

The two phases are said to be in equilibrium when the rate at which water molecules entering the solid state is exactly matched by rate entering the liquid state. The temperature at which this occurs is called the melting point, or freezing point, of water. Note that true phase changes are not considered to be chemical reactions as no intramolecular bonds are broken or formed. 

Nitriles will direct lithiation with non-nucleophilic bases such as LiTMP, particularly in conjuction with another nitrile group . The nitriles presumably act by an acidifying effect alone—no intramolecular N-Li coordination is possible in the intermediate (Scheme 60). 

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