Protonation and Deuteration

Protonation of organometallic intermediates by addition of water or alcohol usually is a trivial reaction of little synthetic interest. However, delocalized anionic intermediates may give different protonation products. Thus, protolysis of cumulenic systems may give acetylenes as well as cumulenes. If only one insomer is formed, the protonation may be synthetically useful  

Such cumulenic derivatives cannot be obtained by isomerization of acetylenic precursors under catalytic conditions, since they are thermodynamically less stable than the acetylenes. Special conditions for the protonation of metallated acetylenic sulfides and metallated enyne amines are described in Refs. [7] and [106] and in Chap. IV, Exp. 19. 

Deuteration can generally be carried out by reaction of D20 or a deuterio-alcohol (e.g. CH3OD or r-BuOD) with the organometallic intermediate. 

The high price of the deuteration reagents requires their economical use. However, stoichiometric amounts often give incomplete conversions. Although deuterations are extremely fast, the hydroxide or alkoxide R OM form complexes with R OD from which D is less readily available. Therefore, at least 100% excess of R OD should be used. If the deuteration has to be carried out at low temperatures, D20, if added to the reaction mixture, solidifies, so that complete deuteration may not be achieved hence, use of a deuterio-alcohol (THF or Et20 solution) is preferred. 

Complications may arise when the normal addition procedure is followed with deuteration reagents. Suppose that thienothiopyran is to be deuterated (in the thiophene ring) 

---

The mesh size was determined from an equivalent network, prepared from a mixture of protonated and deuterated precursors. The radius of gyration of the mesh strands was found to be 25 A, which is identical to the radius of gyration of the uncross-linked precursors. 

The second example deals with dilute solutions of 12-arm stars, where the arm are built up by symmetrical diblocks of protonated and deuterated but otherwise identical monomers [149], Figure 48 displays the reduced relaxation rates r12/Q3- In addition the effective 1/e decay rates of the dynamic structure... 

Table 8. Details of different labelled 12-arm PIP stars (samples 1,2,4 arms of symmetnc diblock of protonated and deuterated PI, respectively)(1) bam = 10 24 cm2 (2) evaluated on the basis of the structural model<3) corrected for the ratio of the viscosities of octane and toluene...

Plenty of other X and Mc scales are available, for these acid media and others. We have published an X scale for aqueous HBr and an Y0 scale for HC1,36 and an X scale for DCIO4,52 although different scales for deuterated acids are unnecessary the scales for the protonated acids can be used, along with the assumption of equal acidity at equal molarity or mole fraction for protonated and deuterated acids,53 which works very well. Marziano, Tomasin... 

Figure 18. Molecular structures of the DNA base-pair model of 7-azaindole. The femtosecond transients and the mass spectra for protonated and deuterated pairs are shown.

The halonium structure 17 was also attributed107 to protonated bromo- and chloromethane, in agreement with theoretical predictions105,106. However, in these two ions an additional interaction (stronger for the bromo than for the chloro compound) is present between the hydrogen bonded to the halogen and the carbon atom107. Protonated iodomethane, on the contrary, structurally resembles protonated methane with the proton bonded to the carbon atom. These conclusions are supported by both MI and CID data for protonated and deuterated halomethanes and by thermochemical data. 

Consider a polymer solution consisting of protonated and deuterated polymers (concentrations CH and CD respectively) that have the same degree of polymerization N. The scattered intensity is proportional to the structure factors for the polymer-polymer correlations SHH(Q), SDD(Q), SHIj(Q), polymer-solvent correlations SpS(Q), and solvent-solvent correlations Sss(Q). The protonated, deuterated and solvent molecule scattering lengths are called aH, aD and as and ap is the average polymer scattering length. The scattered intensity can be expressed in terms of an absolute cross section as ... 

It is clear from infrared and Raman measurements [20,31,33] (see also above) that the interaction between the electrons and the symmetric vibrational modes of TCNQ is in fact so efficient that a significant part of the electronic gap is actually attributable to static molecular distortions [31]. The most important consequence is that the lattice is then less distorted than one would expect from the magnitude of the electronic gap. When such molecular distortions are correctly included in the model, as an external potential of period 2kF, a reasonably good agreement is then obtained with the experimental data for both protonated and deuterated TEA(TCNQ)2 [35,36]. 

The most characteristic feature, however, will be observed in the structure of the vibrational satellites. The change of the electronic charge distribution due to an electronic transition is experienced by the whole molecule, in particular of both the deuterated and the protonated ligands. Thus, the emission spectrum will exhibit ligand satellites of both protonated and deuterated ligands. It is very important that these satellites belong to the same electronic 0-0 transition. 

At high pressures gaseous system most closely resemble the situation in condensed media, and it is instructive to determine the radiative rate constant for this system, and Its variation with temperature. Assuming that internal conversion from Sj is a nonquenchable process which occurs prior to vibrational relaxation from a nonequilibrated state and using results of and 0.j. determined by Cundall and Dunnicliff (105) and values of Tp due to Lockwood (114), the calculated kp values are presented in Table 7 for both CgHg and C Dg. The similarity of rate constants for the protonated and deuterated molecules indicates that the large differences in yield and lifetime for the two isomers are the result of an Isotope effect on a nonradlative transition. 

Measurement of the chemical shift difference between protonated and deuterated acids as a function of pH, essentially as described by eqn (2.8), but for isotopomers, not stereoisomers. 

The equilibrium between the trans and O-inside cis conformers of perhy-dropyrido[l,2-c][l,3]oxazine (20, X = O) was frozen by protonation and deuteration (88MRC748). The ratio of the trans and O-inside cis forms was investigated by and spectra and is tabulated in Table I. H NMR spectra of the hydrochloride salt of c -4fl,8-H-8-methyl- and trans-4a,7-H-... 

Here, and represent the partition functions of the protonated and deuter-ated initial state and and those of the transition state. In order to evaluate... 

Reports on organolithium compounds with internal heteroatom stabilization and their reactions with alkylating agents7 12 -14 are informative for stereoselective protonations and deuter-ations. 

Kolaczkowski (1989) incorporated perdeutero-spheroidene into protonated and deuterated RCs and explored the role of vibrational terms in the mechanism of triplet enagy transfer from the primary donor to the carotenoid. Mechanisms of triplet energy transfer have been postulated to involve specific electronic and/or vibrational states and/or structural changes in the protein to account for the activated nature of the process (Frank et al., 1983, 1993a, 1996 Takiff and Boxer, 1988a,b Kolaczkowski, 1989 Fous and Hoff, 1989). 

Figure 5 shows the AH s calculated from polarimetric data for the various solutions, as a function of Tc. Within the rather sizable experimental errors the data for both the protonated and deuterated solutions can be represented by a single curve. The implication is therefore that differences in AH for PBG(H) and PBG(D) solutions with identical solvent compositions are reflections of changes in Tc rather than a result of deuteration per se. 

Some indication of active-site acidic functionality in P450 dioxygen scission can be revealed by the comparative evaluation of kinetic parameters in protonated and deuterated waters. The use of kinetic solvent isotope effects (KSIEs) has been valuable in the determination of potential proton-linked dioxygen activating enzymes such as P450 -, methane monooxygenase (MMO), ... 

Another very interesting problem concerns the concentration dependents of the effective Flory-Huggins parameter Xeff(. T) that can be extracted from small angle scattering data by fitting Eqs. (37), (46) or (55) to them. It has been found that Xrff (> T) for symmetric mixtures (such as mixtures of protonated and deuterated polyethylene. Fig. 33a) is nearly independent of volume fraction < ) for < ) around <1) but shows a sharp upturn both near and near < ) 1. 

The most common HPLC solvents used for LC NMR are acetonitrile and water. Both protonated and deuterated acetonitrile and water are commercially available and routinely used, where cost is a major consideration in minimizing the utility of deuterated solvents in HPLC experiments. Commonly, a low percentage of trifloroacetic acid (TEA) is also added to the HPLC solvent system to improve the LC peak lineshape. In some cases, a methanol water solvent mixture replaces the water-acetonitrile system if the compound of interest does not behave well (low solubility, aggregation, broad peak shape). If an MS system is attached to the LC-NMR to monitor the molecular weight than formic acid is preferred as a modifier. Table 12.9 provides a Kst of commonly used hyphenated techniques and their advantages and disadvantages. 

Another important statement of French authors from their neutron scattering experiments was that the size of polystyrene strands in dry model networks is equal to the size of the precursor chains dissolved under -conditions (see Table 1.5). At first sight, this result confirms the idea [136, 137], expressed by Flory [138] in the middle of the last century and later picked up by De Gennes [139], that in bulk polymer the chain retains its unperturbed dimension characteristic of its solution in a -solvent. Flory believed to have experimentally confirmed his idea [140]. By analyzing elastic neutron scattering from a mixture of linear protonated and deuterated polyisobutylene with a molecular weight of 48,000+ 3,000 Da, he found that the gyration radii of the macromolecules... 

---