Real Enolates

The NDT Newsgroup and other forums are playing an important role in expediting meeting and communieation among your NDT colleagues on the Internet - Email is the most important tool for that. Not only technical discussions but also business to business or even direct inquiries are today handled via the Internet. Statistics are presented with more information on specific usage.  [c.972]

You have had earlier experience with enols m their role as intermediates m the hydration of alkynes (Section 9 12) The mechanism of enolization of aldehydes and ketones is precisely the reverse of the mechanism by which an enol is converted to a carbonyl compound  [c.759]

Among numerous examples of the role of the chemical structure in tunneling rotation we select just one, connected with the effect of intramolecular hydrogen bond. In acetyl acetone in stable enol form  [c.120]

You have had earlier experience with enols in their role as intermediates in the hydration of alkynes (Section 9.12). The mechanism of enolization of aldehydes and ketones is precisely the reverse of the mechanism by which an enol is converted to a carbonyl compound.  [c.759]

It is important to recognize that an enol is a real substance, capable of independent existence. An enol is not a resonance form of a carbonyl compound the two are constitutional isomers of each other.  [c.761]

Recall that, prior to synthesizing ATP in the phosphoglycerate kinase reaction, it was necessary to first make a substrate having a high-energy phosphate. Reaction 9 of glycolysis similarly makes a high-energy phosphate in preparation for ATP synthesis. Enolase catalyzes the formation of phosphoenolpyruvate from 2-phosphoglycerate (Figure 19.26). The reaction in essence involves a dehydration—the removal of a water molecule—to form the enol structure of PEP. The AG° for this reaction is relatively small at 1.8 kj/mol (Al<.q = 0.5) and, under cellular conditions, AG is very close to zero. In light of this condition, it may be difficult at first to understand how the enolase reaction transforms a substrate with a relatively low free energy of hydrolysis into a product (PEP) with a very high free energy of hydrolysis. This puzzle is clarified by real-  [c.628]

Among the most interesting transient speeies that ean be studied at THz frequeneies are those involving eolleetions of moleeules held together by van der Waals or hydrogen bonding forees. In no small measure this is tnie beeause hydrogen bonds are ubiquitous in nature. From the iey mantles eovering interstellar dust to the nuelei of living eells, hydrogen bonds play enieial roles in the regulation and evolution of both inorganie and living systems. Aeeiirate, fiilly anisotropie, deseriptions of the mtennoleeular forees involved in these and other weak interaetions are therefore assuming an inereasingly pivotal role in modem moleeular seienee,  [c.1254]

It IS important to recognize that an enol is a real substance capable of mdepen dent existence An enol is not a resonance form of a carbonyl compound the two are constitutional isomers of each other  [c.761]

Adhesives. The fundamentals of adhesion have an important role in modem restorative dentistry (see Adhesives). The retention of restorative materials to tooth stmcture, in addition to hoi ding the restoration to the teeth, seals the interface between the tooth and restorative material. Maintenance of this seal reduces pulpal irritation and the potential for recurrent decay. The appHcation of high performance adhesives reduces the need for mechanically retentive cavity designs, thereby minimizing removal of healthy tooth stmcture. Adhesion also plays an important role in hoi ding prosthetic materials to one another. Polymer adhesive materials can be classified as composite or fiUed resin cements, porcelain or ceramic coupling agents, metal coupling agents, or enamel and dentin adhesives.  [c.493]

In the trans-enol form the transition does not occur because of the large tunneling distance for the hydrogen atom (2.8 A). In the cis-form this length decreases to 1 A, but the transition to this form is unfavorable energetically ( — AE 3 kcal/mol). In the transition state the OH bond lies out of plane of the ring. Siebrand et al. [1984] have demonstrated that the experimental curves k iT) and ko(T) can be fitted by the golden-rule formula [see eqs. (5.67) and (5.68)], with the tunneling matrix element modulated by a collinear vibration of frequency 120 cm and reduced mass 15 mn The evaluated tunneling distance for the H atom is 1.8 A. In the framework of the golden-rule approach Siebrand et al. [1984] have also considered several other systems.  [c.110]

In contrast to the alkaloids mentioned so far, heterocyclic mesomeric betaines are defined as neutral conjugated molecules which can be represented only by dipolar structures in which both the negative and the positive charges are delocalized within the rr-electron system (38JCS824, 85T2239). The first heterocyclic mesomeric betaine was prepared unknowingly by Emil Fischer (1882LA316). The real structure remained unknown  [c.71]

Rawal and Kozmin have utilized a Reissert type reac The requisite niiro ketone is prepared by SnAt rea fluoride with ketone silyl enol ether fScheme 10.10.  [c.345]

Emmanuel, K. A. (1999). Weather, Vol. 54 The Power of a Hurricane. Reading, UK Royal Meteorological Society.  [c.94]

The coefficient of thermal expansion is primarily determined by the frit composition, although mill additions can have a minor influence. As a general rule, superior acid and thermal shock resistance obtain with low expansion enamel, and the skill of the frit manufacturer is to obtain good resistance and also to maintain a sufficiently high expansion to prevent distortion of the component (pressing or casting). Several workers have produced a set of factors for expansion in relation to the enamel oxides that constitute the frit, which provides a guide to the frit producer. However, as these factors are derived from a study of relatively simple glasses smelted to homogeneity it must be emphasised that they are only a guide. The effect of substituting certain oxides for others in a standard titanium superopaque enamel is given in Table 16.2. The use of a nickel dip improves adhesion by minimising iron oxide formation, but it should be noted that some iron oxide formation is necessary to produce enamel/metal adhesion. In the commonest methods of testing for adherence to sheet iron, the coated metal is distorted by bending, twisting or impact under a falling weight. In the worst cases the enamel is removed leaving the metal bright and shiny, but in all others a dark coloured coating remains with slivers of fractured enamel adhering to a greater or lesser degree. With cast iron enamelling it is not possible to distort the metal and in this case an assessment of adhesion is obtained by dropping a weight on to the enamel surface and examining for fractures. Erroneous results can obtain in that often thicker enamel coatings appear to be better bonded and resistant to impact, whereas in fact the converse is true. Providing the bond is adequate this test really gives an indication of the strength of the enamel itself.  [c.738]

See pages that mention the term Real Enolates : [c.950]    [c.286]    [c.270]    [c.477]    [c.1061]    [c.116]    [c.66]   
See chapters in:

The molecular modeling workbook for organic chemistry  -> Real Enolates