Revertant

The parent acid is unstable and always reverts to the lactone form shown. It is reconverted to acetoacetic ester by boiling alcoholic potassium hydroxide. Reduced by hydrogen iodide to dimethylpyrone. 

Dewar benzene is a valence isomer of benzene, to which it reverts on heating. 

PPha, pyridine) organic groups (olefines, aromatic derivatives) and also form other derivatives, e.g. halides, hydrides, sulphides, metal cluster compounds Compounds containing clusters of metal atoms linked together by covalent (or co-ordinate) bands, metaldehyde, (C2H40) ( = 4 or 6). A solid crystalline substance, sublimes without melting at I12 1I5" C stable when pure it is readily formed when elhanal is left in the presence of a catalyst at low temperatures, but has unpredictable stability and will revert to the monomer, ft is used for slug control and as a fuel. 

Cobalt(II) compounds are often incorporated in the gel. When the gel has absorbed a fair amount of moisture it will turn pink but will revert to blue on heating. 

The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

Because of the charged nature of many Langmuir films, fairly marked effects of changing the pH of the substrate phase are often observed. An obvious case is that of the fatty-acid monolayers these will be ionized on alkaline substrates, and as a result of the repulsion between the charged polar groups, the film reverts to a gaseous or liquid expanded state at a much lower temperature than does the acid form [121]. Also, the surface potential drops since, as illustrated in Fig. XV-13, the presence of nearby counterions introduces a dipole opposite in orientation to that previously present. A similar situation is found with long-chain amines on acid substrates [122]. 

Perhaps the most fascinating detail is the surface reconstruction that occurs with CO adsorption (see Refs. 311 and 312 for more general discussions of chemisorption-induced reconstructions of metal surfaces). As shown in Fig. XVI-8, for example, the Pt(lOO) bare surface reconstructs itself to a hexagonal pattern, but on CO adsorption this reconstruction is lifted [306] CO adsorption on Pd( 110) reconstructs the surface to a missing-row pattern [309]. These reconstructions are reversible and as a result, oscillatory behavior can be observed. Returning to the Pt(lOO) case, as CO is adsorbed patches of the simple 1 x 1 structure (the structure of an undistorted (100) face) form. Oxygen adsorbs on any bare 1 x 1 spots, reacts with adjacent CO to remove it as CO2, and at a certain point, the surface reverts to toe hexagonal stmcture. The presumed sequence of events is shown in Fig. XVIII-28. 

The pressure coefficients can be related to the volume coefficients by reverting the series and one finds that... 

This series oan be reverted and the resulting equation is very simple ... 

Reverting this series and simplifying yields the final result in powers of t... 

It reverts to the unspin-orbit modified value, = —tt, for paths such that kr A, but vanishes as r 0. 

Reverting to the vibronic structure, the operator j again commutes with H, and the analogue of the lower adiabatic eigenstate of j in Eq. (66) becomes... 

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

In order to overcome these weaknesses, Pople and co-workers reverted to a more complete approach that they first proposed in 1965 [14], neglect of diatomic differential overlap (NDDO). In NDDO, all four-center integrals (pv are considered in which p and v are on one center, as are 2 and cr (but not necessarily on the same one as and v). Furthermore, integrals for which the two atomic centers are diEFer-ent are treated in an analogous way to the one-center integrals in INDO, resulting... 

The characteristic property of aliphatic nitrocompounds of the type RCHiKOj and RjCHNO, is that they are pseiido cids, I. e., whereas they are neutral in the normal form (A), they are able by tautomeric change under the influence of alkali to give the acidic hydroxy form (B) which thus in turn gives the sodium salt (C). When this sodium salt is treated with one equivalent of hydrochloric acid, the acid form (B) is at once regenerated, and then more slowly reverts to the more stable normal form (A). 

Reaction of Diphenylnitrosoamine. Carry out Liebermann s Nitroso Reaction as described for phenol (p. 340), but use about 0 05 g. of the nitrosamine instead of the one crystal of sodium nitrite, and finally add only 3-4 drops of sulphuric acid. The deep greenish-blue colour is obtained, becoming red on dilution and reverting to blue on being made alkaline. 

Graphite exists in two forms alpha and beta. These have identical physical properties, except for their crystal structure. Naturally occurring graphites are reported to contain as much as 30% of the rhombohedral (beta) form, whereas synthetic materials contain only the alpha form. The hexagonal alpha type can be converted to the beta by mechanical treatment, and the beta form reverts to the alpha on heating it above lOOOoC. 

Fluorine addition to alkenes is a violent reaction difficult to control and accompa med by substitution of hydrogens by fluorine Vicinal diicxlides on the other hand tend to lose I2 and revert to alkenes making them an infrequently encountered class of compounds... 

Protonation of the carbonyl oxygen activates the carbonyl group toward nucleophilic addition Addition of an alcohol gives a tetrahedral inter mediate (shown m the box m the preceding equation) which has the capacity to revert to starting materials or to undergo dehydration to yield an ester... 

Once formed the tetrahedral intermediate can revert to starting materials by merely reversing the reactions that formed it or it can continue onward to products In the sec ond stage of ester hydrolysis the tetrahedral intermediate dissociates to an alcohol and a carboxylic acid In step 4 of Figure 20 4 protonation of the tetrahedral intermediate at Its alkoxy oxygen gives a new oxonium ion which loses a molecule of alcohol m step 5 Along with the alcohol the protonated form of the carboxylic acid arises by dissocia tion of the tetrahedral intermediate Its deprotonation m step 6 completes the process... 

The two OH groups m the tetrahedral intermediate are equivalent and so either the labeled or the unlabeled one can be lost when the tetrahedral intermediate reverts to ethyl benzoate Both are retained when the tetrahedral intermediate goes on to form benzoic acid... 

Enolization of an aldose or a ketose gives an enediol Enediols can revert to aldoses or ketoses with loss of stereochemical integrity at the a carbon atom... 

However, this form becomes repulsive for r - rg > 2/3 CS, so it is unsuitable for bond lengths significantly larger than equilibrium. In the MM2 program, this is avoided by temporarily setting CS to zero, reverting to a quadratic form, which leads to discontinuities in the potential surface that are unacceptable for geometry optimi-... 

The reverse of coagulation in which a coagulated precipitate reverts to smaller particles. 

Because of this spin selection rule, atoms which get into the lowest triplet state, 2 Si, do not easily revert to the ground 1 state the transition is forbidden by both the orbital and spin selection rules. The lowest triplet state is therefore metastable. In a typical discharge it has a lifetime of the order of 1 ms. 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

The details of the commercial preparation of acetal homo- and copolymers are discussed later. One aspect of the polymerisation so pervades the chemistry of the resulting polymers that familiarity with it is a prerequisite for understanding the chemistry of the polymers, the often subde differences between homo- and copolymers, and the difficulties which had to be overcome to make the polymers commercially useful. The ionic polymerisations of formaldehyde and trioxane are equiUbrium reactions. Unless suitable measures are taken, polymer will begin to revert to monomeric formaldehyde at processing temperatures by depolymerisation (called unsipping) which begins at chain ends. 

An electric dipole consists of two equal and opposite charges separated by a distance. AH molecules contain atoms composed of positively charged nuclei and negatively charged electrons. When a molecule is placed in an electric field between two charged plates, the field attracts the positive nuclei toward the negative plate and the electrons toward the positive plate. This electrical distortion, or polarization of the molecule, creates an electric dipole. When the field is removed, the distortion disappears, and the molecule reverts to its original condition. This electrical distortion of the molecule is caHed induced polarization the dipole formed is an induced dipole. 

Electro osmosis often accompanies electrophoresis. It is the transport of Hquid past a surface or through a porous soHd, which is electricaHy charged but immovable, toward the electrode with the same charge as that of the surface. Electrophoresis reverts to electroosmotic flow when the charged particles are made immovable if the electroosmotic flow is forcibly prevented, pressure builds up and is caHed electroosmotic pressure. 

Ammonium fluoride is a white, deflquescent, crystalline salt. It tends to lose ammonia gas to revert to the more stable ammonium bifluoride. Its solubiUty in water is 45.3 g/100 g of H2O at 25°C and its heat of formation is —466.9 kJ/mol ( — 116 kcal/mol). Ammonium fluoride is available principally as a laboratory reagent. If it is needed in large quantities, one mole of aqueous ammonia can be mixed with one mole of the more readily available ammonium bifluoride (1). 

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