Reverse transformation

Agnew S F, Swanson B I, Jones L FI, Mills R L and Sohiferl D 1983 Chemistry of nitrogen oxide (N2O4) at high pressure observation of a reversible transformation between moleoular and ionio orystalline forms J. Phys. Chem. 

Ammonium chloride [12125-02-9] NH Q, ammonium bromide [12124-97-9] NH Br, and ammonium iodide [12027-06-4] NH I, are crystalline, ionic compounds of formula wts 53.49, 97.94, and 144.94, respectively. Their densities d systematically foUow the increase in formula weight 1.53, 2.40, and 2.52. AH three exist in two crystal modifications (10) the chloride, bromide, and iodide have the CsQ stmcture below temperatures of 184.5, 137.8, and — 17.6°C, respectively each reversibly transforms to the NaQ. stmcture at higher temperatures. 

Fig. 1. Schematic of the hysteresis loop associated with a shape-memory alloy transformation, where M. and Afp correspond to the martensite start and finish temperatures, respectively, and and correspond to the start and finish of the reverse transformation of martensite, respectively. The physical property can be volume, length, electrical resistance, etc. On cooling the body-centered cubic (bcc) austenite (parent) transforms to an ordered B2 or E)02...

Fig. 2. The shape-memory process, where Tis temperature, (a) The cycle where the parent phase undergoes a self-accommodating martensite transformation on cooling to the 24 variants of martensite. No macroscopic shape change occurs. The variants coalesce under stress to a single martensite variant, resulting in deformation. Then, upon heating, they revert back to the original austenite crystallographic orientation, and reverse transformation, undergoing complete recovery to complete the cycle, (b) Shape deformation. Strain recovery is typically ca 7%.

Poly(vinyl alcohol) [9002-89-5] was discovered through the addition of alkaU to a clear alcohoHc solution of poly(vinyl acetate), which resulted in the ivory-colored poly(vinyl alcohol) (4). The same discovery has been made by studying the reversible transformation between poly(vinyl alcohol) and poly(vinyl acetate) via esterification and saponification (5). The first scientific reports on poly(vinyl alcohol) were pubUshed in 1927 (6,7). 

Gibbs s fundamental relation governing an infinitesimal, reversible transformation can be written... 

Note that the definition of R is arbitrary. However, the present choice seems simplest and has a transparent physical interpretation. The work done by the system in an infinitesimal reversible transformation at constant S, N, A, s, and ayiy is given by... 

Two situations are considered which differ in the number of constraints imposed. In the first one the shear strain in x and y directions is fixed, infinitesimal, reversible transformations are governed by the thermodynamic potential [see Eq. (9)], and X is the relevant partition function [see Eq. (52)]. Here the shear stress is computed as a function of the registry... 

The relative stability of lithiated thiopyrans seems to depend upon the heterocyclic ring substitution. Thus, a-lithiated 2,6-diphenyl-2//-thiopyran 16 rearranges into the y-lithiated derivative 17 (Scheme 5) (82JOC680), while the reverse transformation occurs on lithiation of 2,6-diphenyl-4-diethylphosphonylthiopyran (80JOC2453). 

Whereas the transformations thietane - thietane oxide- thietane dioxide are easy to perform192, as is the reverse transformation thietane dioxides ->thietanes188, no method of reducing the sulfonyl group to a sulfoxy group is available as yet. 

Bifunctional monomers capable of forming six- or seven-membered rings condense variably, depending upon the particular monomer. The products normally obtained in the absence of diluent in various representative bifunctional condensations are listed in Table IX for unit lengths of six and seven members. The term interconvertibility refers to the reversible transformation between the ring and the linear polymer. Several of the six-membered units (Table IX) prefer the ring form exclusively, but most of them yield both products, or at any rate the ring and chain products are readily interconvertible. Seven-membered units either yield linear polymers exclusively, or, if the cyclic monomer is formed under ordinary conditions, it is convertible to the linear polymer. 

Giordano, Michael J. Reverse transformation Beroalde de Verville s parody of Paracelsus in LeMoyen de parvenir an alchemical language of skepticism in the French Baroque. Renaissance Q 56, no. 1 (Spring 2003) 88-137. 

As McWeeny [13] showed by the reverse transformation of Equation (40), E can always be factored into... 

Kaupp and Prinzbach have shown that the sum of the quantum yields for the forward and reverse transformations of a number of norbornadienes and quadricyclanes is about unity(115 117) ... 

Chatani42,43 has shown that if the hexagonal inclusion compounds are cooled many of them undergo a reversible transformation into a low-temperature form with the orthorhombic space group These phase transitions take place over a... 

Reversible reactions are those in which appreciable quantities of all reactant and product species coexist at equilibrium. For these reactions the rate that is observed in the laboratory is a reflection of the interaction between the rate at which reactant species are transformed into product molecules and the rate of the reverse transformation. The ultimate composition of the systems in which such reactions occur is dictated not by exhaustion of the limiting reagent, but by the constraints imposed by the thermodynamics of the reaction. 

Photochromic FRET using as acceptors the photochromic compounds such as spiropyrans [36]. They have the ability to undergo a reversible transformation between two different structural forms in response to illumination at appropriate wavelengths. These forms may have different absorption (and in some cases,... 

One can further conclude that that these two Gaussian distributions are symmetrically located on the upper and lower sides of AA, and the free energy difference A A, the mean work W OF, for the forward and — W >0 for the reverse transformation) and the variance of work obey the following relationships ... 

The choice of metals has been narrowed down to Si and A1 for this group of experiments. The approximate potentials of the reversible transformation (subject of polarization) of C into LiC6 is taking place in the range of 0.6 0.01 V (vs Li/Li+) while for conversion of Si into Li22C5 it is... 

They demonstrated that copper deposition on Ag(100) produces a BCC structure in the first eight layers of copper, which is then reversibly transformed to the FCC structure on addition of one more layer [119]. 

The reaction of 18 and 19 with phosphorus ylides occurs as a stepwise process. Betaine (21) can be isolated when (Me2SiS)3 reacts with Ph3P=CHMe in a 3 2 ratio of the reactants (Scheme 11). This substance is quite stable in the solid state but on dissolving in pyridine it is reversibly transformed into a mixture of 20k and (Me2SiS)3. The equilibrium concentration of 21 in a solution at room temperature is at most 28% according to the NMR data, and the addition of one more equivalent of Ph3P=CHMe to the solution results in the quantitative transformation of 21 into 20k. 

As has already been discussed (Section m.B.3) we were able to demonstrate that the three C3H2 isomers cyclopropenylidene (2), propargylene (36), and vinylidenecarbene (37), interconvert photochemically in low-temperature matrices. Unlike 36 vinylidenecarbene (37) was predicted to be a singlet.108-110 To aid the spectroscopic identification of S-37 we calculated (MP2/6-31G ) IR frequencies and intensities of this species.26 Comparison with the experimental IR spectrum (most intense band at 1952 cm-1) confirmed the allenic structure S-37. For T-37 a completely different IR spectrum was expected. An additional structural proof for S-37 was its reversible transformation into the other two C3H2 isomers S-2 and T-36. 

For Hamiltonians invariant under rotational and time-reversal transformations the corresponding ensemble of matrices is called the Gaussian orthogonal ensemble (GOE). It was established that GOE describes the statistical fluctuation properties of a quantum system whose classical analog is completely chaotic. 

As shown in Scheme 16, the A-oxidations of 112 can yield 4-oxides 113 and/or 5-oxides 114 can be formed. In some special cases (e.g., if R3 = Br), formation of exclusively 114 was experienced. The reverse transformation was also carried out reduction of the A-oxides (113, 114) by triethylphosphite or Zn/acetic acid yielded the deoxy compound 112. 

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