Triplet nature

Again the left superscript indicates the spin-triplet nature of the arrangement. The letter A means that it is spatially (orbitally) one-fold degenerate and it is upper-case because we describe two-electron wavefunctions. The subscript is g because the product of d orbitals is even under the octahedral centre of inversion, and the right subscript 2 must remain a mystery for us once again. 

It should be noted that Gaussian multiplication can severely distort peaks and also reduce signal-to-noise of the spectrum so it is not a good idea to do this if you have a very weak spectrum to start with. Spectrum 4.1 shows a real case where Gaussian multiplication has been able to resolve a triplet. Note that it is possible to just make out the triplet nature of the peak in the unmultiplied spectrum - Gaussian multiplication helps verify this and also allows us to measure the splitting pattern. 

Another important technique was based on the observation that synthetic trinucleotides induced the binding to ribosomes of tRNA molecules that were "charged" with their specific amino acids 38/39 For example, the trinucleotides UpUpU and ApApA stimulated the binding to ribosomes of 14C-labeled phenylalanyl-tRNA and lysyl-tRNA, respectively. The corresponding dinucleotides had no effect, an observation that not only verified the two codons but also provided direct evidence for the triplet nature of the genetic code. Another powerful approach was the use of artificial RNA polymers, synthesized by combined chemical and enzymatic approaches.40 For example, the polynucleotide CUCUCUCUCU led to the synthesis by ribosomes of a regular alternating polypeptide of leucine and serine. 

Before the triplet nature of codons had been established, Crick and associates used frame-shift mutations in a clever way to demonstrate that the genetic code did consist of triplets of nucleotides.7 55/55a Consider what will happen if two strains of bacteria, each containing a frame-shift mutation (e.g., a -1 deletion), are mated. Genetic recombination can occur to yield mutants containing both of the frame-shift mutations. 

In the past few years the ESR technique has been applied to demonstrate the triplet nature of many highly reactive organic biradicals and of various metastable photoexcited states, to estimate the rates of their decay, and to evaluate their electronic distribution. These metastable states are normally produced and observed either frozen in glassy matrices at 77°K or aligned in a host crystal. Spectra have also been obtained of triplet species dissolved in a translucent plastic. 

The photoequilibrium (114) (118) (see section III-A) and the irreversible rearrangement (118) - (120) contribute additional examples of photochemical isomerizations of cyclopropyl ketones to enones. The triplet nature of these isomerizations of (118) has been demonstrated by complete... 

When the enone chromophore of the diketone (148) is excited selectively using 2537 A-light, a smooth conversion to the two stereoisomeric cyclopropyl diketones (149) and (150) takes place exclusively.27,28,44 Experiments with the 4a-deuteriomethyl analog of (148) establish a stepwise reaction sequence with the diradicals (151) [- (149)] and (152) [-> (150)] as the most likely intermediates formed in the primary photoprocess. Total quenching with naphthalene indicates the triplet nature of the reaction. 

The photolysis of the 4-alkylidene-l-pyrazoline (94) gives rise to two isomeric methylene cyclopropanes (95 and 96).76 The available evidence points to the intermediacy of a trimethylenemethyl species (97) in the triplet state which can cyclize in three ways. The same species is postulated in the photolysis of a series of 4-alkylidene-l-pyrazoline-3-carboxylates.77 This appears to be a general route to derivatives of trimethylenemethyl trimethylenemethyl itself has been generated from 4-methylene-1-pyrazoline and the triplet nature of the intermediate identified by electron spin resonance (ESR) spectroscopy.78... 

The quantum mechanical methods described in this book are all molecular orbital (MO) methods, or oriented toward the molecular orbital approach ab initio and semiempirical methods use the MO method, and density functional methods are oriented toward the MO approach. There is another approach to applying the Schrodinger equation to chemistry, namely the valence bond method. Basically the MO method allows atomic orbitals to interact to create the molecular orbitals of a molecule, and does not focus on individual bonds as shown in conventional structural formulas. The VB method, on the other hand, takes the molecule, mathematically, as a sum (linear combination) of structures each of which corresponds to a structural formula with a certain pairing of electrons [16]. The MO method explains in a relatively simple way phenomena that can be understood only with difficulty using the VB method, like the triplet nature of dioxygen or the fact that benzene is aromatic but cyclobutadiene is not [17]. With the application of computers to quantum chemistry the MO method almost eclipsed the VB approach, but the latter has in recent years made a limited comeback [18],... 

An interesting use of removable chiral auxiliaries in photocycloadditidl reactions concerns imminium salts. With cyclic enones, the observed asymmetri induction does not result from an approach of the double bonds in parallel plane because of the triplet nature of the reactive excited state. In contrast, the corn sponding imminium salts react through their singlet excited state, and a ... 

Illg of Pt(2-thpy)2 and thus manifest additionally the triplet nature of this set of sublevels. ... 

Consequently, they lead to the insertion or deletion of one or more base pairs. The effect of such mutations is to alter the reading frame in translation, unless an integral multiple of three base pairs is inserted or deleted. In fact, the analysis of such mutants contributed greatly to the revelation of the triplet nature of the genetic code. 

A distinction between the cis and trans geometries of methylphosphine-transition-metal complexes has been possible by considering the triplet nature of the methyl proton signal arising from the virtual coupling in the rmns -isomers, (ref. 8a, p. 293). A similar effect is observed in the n.m.r. spectra, and the effect is not limited to methylphosphines. ... 

The most extensive efforts to develop the OLED-based sensor platform have focused on PE-based gas-phase and dissolved O2 (DO) sensors. Such sensors, which have been studied for many years, are based on the efficient quenching of the PL of dyes such as Ru complexes and Pt or Pd porphyrins by collisions with O2 molecules the sensitivity to O2 is due to the nearly unique triplet nature of the ground state of O2. In an ideal homogeneous matrix, the O2 concentration [O2I is related to the steady-state PL intensity I and the PL decay time x by the Stern-Volmer (SV) equation ... 

While good results were obtained with the ADSQC technique, the authors note that artefacts of a triplet nature were observed in F. as suggested by the analysis of Zangger and Armitage in their report of the accordion-HMQC experiment (see p. 44). - To address this potential deficiency, Hadden et al. utilized randomization of the variable delay table to provide essentially complete suppression of the artefacts observed in the ADSQC. The modified experiment has been given... 

A variety of photochemical reactions have been found for both the singlet and triplet excited states of p,Y-unsaturated ketones. It has been the molecular rearrangements, however, which appear to be the unique character of this grouping, rearrangements which are controlled by the singlet or triplet nature of the excited state. 

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