Double bond

The heat of hydrogenation of an alkyne is greater than twice the heat of hydro genation of an alkene When two moles of hydrogen add to an alkyne addition of the first mole (triple bond double bond) is more exothermic than the second (double bond single bond)... 

Double bonds m the mam chain are signaled by the ending enow acid and their position IS designated by a numerical prefix Entries 6 and 7 are representative carboxylic acids that contain double bonds Double bond stereochemistry is specified by using either the cis-trans or the E-Z notation... 

Because the integrity of the dihydrothiazine ring and its C-4 carboxyl substituent is crucial to useful antimicrobial activity, reactions involving this part of the cephalosporin molecule are usually undesirable. The possibilities for sulfur oxidation or alkylation, substitution at C-2 which is adjacent to both sulfur and a double bond, double bond isomerization and addition reactions, and the influence of a free carboxylic acid must all be considered in designing reactions to selectively modify other cephalosporin functionalities. 

Atom Single bond Double bond Triple bond... 

Carbon has six electrons around the atomic core as shown in Fig. 2. Among them two electrons are in the K-shell being the closest position from the centre of atom, and the residual four electrons in the L-shell. TTie former is the Is state and the latter are divided into two states, 2s and 2p. The chemical bonding between neighbouring carbon atoms is undertaken by the L-shell electrons. Three types of chemical bonds in carbon are single bond contributed from one 2s electron and three 2p electrons to be cited as sp bonding, double bond as sp and triple bond as sp from the hybridised atomic-orbital model. 

Doppel aus6chlag, m. double throw or deflection (as of a balance needle), -bier, n. double beer, -bild, n. double image, -bindung, /. double bond, double linkage, -boden, m. double bottom, false bottom jacket, -bogen, m. double bend U-tube, XJ-pipe. doppel-borsauer, a. biborate (tetraborate) of. 

Figure 12.15 The four regions of the infrared spectrum single bonds to hydrogen, triple bonds, double bonds, and fingerprint.

The Dependence of Interatomic Distance on Single Bond-Double Bond Resonance1... 

Through these four points we draw a smooth curve, as shown in Fig. 1, which we accept as representing the dependence of carbon-carbon interatomic distance on double-bond character for single bond-double bond resonance. We believe that by a suitable translation and a change of vertical scale (to give the correct end-points) the same function can fee used for bonds between other atoms, and probably also for double bond-triple bond resonance. This use of the curve will be illustrated below. 

Fig. 1.—The empirical function expressing the dependence of carbon-carbon interatomic distance on bond character for single bond-double bond resonance.

Dec., 1935 Single Bond-Double Bond Resonance and Interatomic Distances 2707... 

The Dependence of Bond Angles on Single Bond-Double Bond Resonance.—In a molecule such as phosgene or 1,1-dichloroethylene the value 125°16 for the angle Cl-C-0 (0) is predicted by the theory of the tetrahedral carbon atom in case that the C-Cl bonds have no double bond character. If the double bond resonates equally among all three positions, giving the Cl-C bond one-third double bond character, we expect from symmetry... 

Fig. 8.—Curve showing the dependence of carbon-carbon bond distance on the relative degree of single-bond-double-bond character.

The determination of values of interatomic distances in molecules has been found to provide much information regarding electronic structure, especially in the case of substances which resonate among two or more valence-bond structures. The interpretation of interatomic distances in terms of the types of bonds involved is made with use of an empirical function formulated originally for single bond-double bond resonance of the carbon-carbon bond.1 There are given in this... 

First we need to locate the part of the molecule where resonance is an issue. Remember that we can push electrons only from lone pairs or bonds. We don t need to worry about all bonds, because we can t push an arrow from a single bond (that would violate the first commandment). So we only care about double or triple bonds. Double and triple bonds are called pi bonds. So we need to look for lone pairs and pi bonds. Usually, only a small region of the molecule will possess either of these features. 

Where does the double bond form This is a question of regiochemistry. The way we distinguish between these two possibilities is by considering how many groups are attached to each double bond. Double bonds can have anywhere from 1 to 4 groups attached to them ... 

Look at your ball-and-stick model sets. Identify the different pieces that represent atoms, single bonds, double bonds, and triple bonds... 

The unusual l-sila-l,2-diol (CH2=CH)CH(OH)SiPh2OH, prepared by hydrolysis of the acylsilane (CH2=CH)C(0)SiHPh2, has a structure comprising hydrogen-bonded double chains as shown in Fig. 9. Only COH - HOSi hydrogen bonds are present, with the bonds between the chains being shorter than those that build up the chain, 2.666 and 2.739 A, respectively (131, 210). 

Fig. 9. The hydrogen-bonded double chain structure of (CH2=CH)CH(0H)SiPh20H with hydrogen atoms omitted for clarity. Drawn using coordinates taken from the Cambridge Crystallographic Database.

Single bond Double bonds Triple bond Two single bonds... 

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