A slightly more complex scheme

This is a typical inorganic mechanism where there is a pre-equilibrium formation of an ion pair or complex, followed by reaction to product, e.g. 

The forward step of the reversible reaction is second order, and this poses the usual problems. 

Normally one of the reactants is held in excess, and the reaction is studied under pseudo-first order conditions, when 

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A slightly more complex Scheme is required for preparation of an antihistaminic agent bearing a secondary amine, e. g., tofenacin (32). In the synthesis of tofenacin, alkylation of the benzhydrol (29) with ethyl bromoacetate affords the alkoxy ester (30) saponification followed by conversion to the methylamide gives (31), which is reduced with lithium aluminum hydride to complete the synthesis of 32. 10... 

In a slightly more complex scheme, aolO ") is assumed to depend exponentially on Vox, the volume occupied by an oxide ion, as proposed by Bussmann etal The parameter Vox is easily calculated for all compounds whose structure is known. Then... 

Coombes and Katchalski [29] have considered a slightly more complex version of this mechanism in which a second propagation coefficient operates above a critical degree of polymerization. Katchalski et al. [30] calculated the molecular weight distribution obtained in a system following scheme (12) but also including a bimolecular termination step. Various authors have analysed more complex systems in which the initiator is a polymeric species. Thus Gold [31] has shown that initiation by a poly a-amino acid with a Poisson distribution leads to a polymeric product with an over-all Poisson distribution, and Katchalski et al. [32] demonstrated that in multichain polymers synthesized from polyfunctional initiators Poisson distributions also arise. 

A slightly more complex application of a Povarov reaction in total synthesis is the preparation of martinellic acid 504, reported by Batey in 2002 (Scheme 13.107) [197b]. Using the Povarov reaction, it was possible to bnild the highly snbstituted 1,2,3,4-tetrahydroquinoline core 503 in only two steps with good diastereoselectivity. 

It is not exactly understood how the mixed ligand Rh/dppb/PPh3 catalyst system functions. Matsumoto proposed that the arm-on, arm-off equilibrium shown in Scheme 12 is operational. A species such as (5) would function much like a normal HRh(CO)(PPh3)2 catalyst, but the ability to reform the chelate to form a slightly more electron-rich complex (6) would tend to inhibit alkene isomerization and/or degradation reactions which require 16e unsaturated species. P NMR studies of Rh/chelating phosphine complexes indicate that a variety of species can form, the most dominant of which are... 

A motif found in the majority of alkali metal stabilized carbanion crystal structures is a nearly planar four-membered ring (13) with two metal atoms (M ) and two anions (A ), i.e. dimer. This simple pattern is rarely observed unadorned as in (13), yet almost every alkali metal and alkaline earth carbanion aggregate can be built up from this basic unit The simplest possible embellishment to (13) is addition of two substituents (S) which produces a planar aggregate (14). Typically the substituents (S) in (14) are solvent molecules with heteroatoms that serve to donate a lone pair of electrons to the metal (M). Only slightly more complex than (14) is the four coordinate metal dimer (15). Often the substiments (S) in (15) are joined by a linear chain. The most common of these chains are tetramethylethylenediamine (TMEDA) or dimethoxyethane (DME) so that the spirocyclic structure (16) ensues. Alternatively the donors (S) in (16) have been observed as halide anions (X ) when the metal (M ) is a divalent cation, e.g. (17) or (18). Obviously, the chelate rings found in (16) are entropically favorable relative to monodentate donors (S) in (14), (15), (17) or (18) (Scheme 2). 

Because of the relatively small outer diameter of an NMR autoclave, the insulation separating the heating elements from the inner wall of the pressure vessel is of critical importance. This insulation must meet the conflicting requirements of low thermal conductivity and low permeabU-ity to convection in the pressure medium. In one scheme, the insulation consists of a layered structure formed by a roll of 0.025 mm molybdenum foil. The layers were separated with small spacing by 0.05 mm pimples embossed on the foil. With this insulation, a sample temperature of 1500 =C at 90 bar can be obtained with 450 W of DC power. A more efficient, but slightly more complex variation uses layers of molybdenum foil separated by thin sheets of alumina cloth. 

If one considers a monomer of slightly more complexity, the permutations of possible structures are even larger. Consider for example, the monomer chloroprene (2-chloro-1,3-butadiene, 3, Scheme 16.2). Chloroprene is polymerized by free radical emulsion polymerization to form polychloro-prene, or neoprene rubber. Neoprene is one of the oldest synthetic rubbers, and is used when higher performance is needed than can be provided by the lower cost styrene butadiene rubber (SBR). Being a butadiene derivative, chloroprene contains two conjugated double bonds. Polymerization takes place by the opening of one double bond the second is less reactive. Polymerization results in one of four possible structures. The trans-1,4 (4, Schane 16.2) structure accounts for approximately 87% of the polymer imits at dO C [2],... 

Scheme for the oxidation of complex 32 (Scheme 15.10). Our rationale was that complex 32 ought to comprise a closo (fully deltahedral) framework by those counting rules. The loss of an electron to give 32+ was thus followed by a subtle polyhedral rearrangement to connect the trans-facial boron and carbon atoms. The new closo geometry 32 + displayed a slightly more cathodic response on the return CV scan, the consequence of which was to reopen the cage back to the isonido geometry.

Typical aryl-aryl coupling reactions that utilize catalytic amounts of Ni(II) salts are outlined in Scheme 12.24. Zinc metal was used to reduce Ni(II) to the cataly tically active Ni(0) species in the homocoupling of dimethoxypyridine 108 and the efficient synthesis of dimer 109 (Eq. 12.24-1) [88]. Alternatively, nickel salts can also efficiently be reduced by means of electrochemical methods. As shown in Equation 12.24-2, Troupel and coworkers were able to recover Ni(0) on a steel electrode and isolated the coupling products in excellent yield [89]. Comparable studies were carried out with slightly more complex substrates and confirmed that... 

The scheme for a B.P. temperature calculation follows the same approach. It is, however, slightly more complex because a method for generating new temperature estimates is needed. 

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