Carbonyl group dipole

The negative cyanide ion is attracted to the positive end of the carbonyl group dipole. 

Miljkovic et al. [10] assumed that a similar situation must exist in case of oxo sugar 21 where the conformation is probably destabilized due to the strong dipolar interaction between the equatorial electronegative C3 methoxy and the polarized C4 carbonyl group dipoles which are in this conformation coplanar and equatorially oriented. Consequently, the oxo sugars 21 and 22, at —80 °C, most likely adopt either a half-chair conformation 31 or a conformation 30 which is between the 21 and the half-chair conformation 31 as shown in Fig. 1.6. 

Coulombic Terms. Coulombie energy of interaetion arises from permanent dipoles within the molecule to be modeled, for example, the partial - - and — charges within a carbonyl group... 

The carbonyl group makes aldehydes and kefones rafher polar molecules dipole momenfs fhaf are subsfanfially higher fhan alkenes... 

In general aldehydes and ketones have higher boiling points than alkenes because they are more polar and the dipole-dipole attractive forces between molecules are stronger But they have lower boiling points than alcohols because unlike alcohols two carbonyl groups can t form hydrogen bonds to each other... 

The carbonyl group withdraws rr electron density from the double bond and both the carbonyl carbon and the p carbon are positively polarized Their greater degree of charge separation makes the dipole moments of a p unsaturated carbonyl compounds signifi cantly larger than those of comparable aldehydes and ketones... 

There are at least two mechanisms available for aziridine cis-trans isomerism. The first is base-catalyzed and proceeds via an intermediate carbanion (235). The second mechanism can be either thermally or photochemically initiated and proceeds by way of an intermediate azomethine ylide. The absence of a catalytic effect and interception of the 1,3-dipole intermediate provide support for this route. A variety of aziridinyl ketones have been found to undergo equilibration when subjected to base-catalyzed conditions (65JA1050). In most of these cases the cis isomer is more stable than the trans. Base-catalyzed isotope exchange has also been observed in at least one molecule which lacks a stabilizing carbonyl group (72TL3591). 

A number of groups have criticized the ideas of Dauben and Noyce, especially the concept of PDC. Kamernitzsky and Akhrem, " in a thorough survey of the stereochemistry of addition reactions to carbonyl groups, accepted the existence of SAC but not of PDC. They point out that the reactions involve low energies of activation (10-13 kcal/mole) and suggest that differences in stereochemistry involve differences in entropies of activation. The effect favoring the equatorial alcohols is attributed to an electrostatic or polar factor (see also ref. 189) which may be determined by a difference in the electrostatic fields on the upper and lower sides of the carbonyl double bond, connected, for example, with the uncompensated dipole moments of the C—H bonds. The way this polar effect is supposed to influence the attack of the hydride is not made clear. 

Let us consider the separation of polymethylmethacrylate (PMMA) on a nonmodified silica column as an example. In THE (medium polar eluent) the PMMA eludes in size exclusion mode because the dipoles of the methylmethacrylate (MMA) are masked by the dipoles of the THE. Using the nonpolar toluene as the eluent on the same column, the separation is governed by adsorption because the dipoles of the carbonyl group in the PMMA will interact with the dipoles on the surface of the stationary phase. The separation of PMMA in the critical mode of adsorption can be achieved by selecting an appropriate THF/toluene mixture as the eluent. In this case all PMMA samples... 

The carbonyl group makes aldehydes and ketones rather polar molecules, with dipole moments that are substantially higher than alkenes. 

Chloroketone (33) prefers to adopt the axial conformation (33a) because of dipole repulsion between C-Cl and C=0, The less hindered side of the carbonyl group is therefore trana to the chlorine giving (35) in the right conformation (35a) - trans diaxlal - for rearrangement. 

The reacting aldehyde displaces the oxazolidinone oxygen at the tetravalent boron in the reactive TS. The conformation of the addition TS for boron enolates is believed to have the oxazolidinone ring oriented with opposed dipoles of the ring and the aldehyde carbonyl groups. 

These are essentially electron redistributions that can take place in unsaturated, and especially in conjugated, systems via their n orbitals. An example is the carbonyl group (p. 203), whose properties are not accounted for entirely satisfactorily by the classical formulation (21a), nor by the extreme dipole (21b) obtainable by shift of the n electrons ... 

There are two important rhodium-catalyzed transformations that are broadly used in domino processes as the primary step. The first route is the formation of keto carbenoids by treatment of diazo keto compounds with Rh11 salts. This is then followed by the generation of a 1,3-dipole by an intramolecular cyclization of the keto carbenoid onto an oxygen atom of a neighboring keto group and an inter- or intramolecular 1,3-dipolar cycloaddition. A noteworthy point here is that the insertion can also take place onto carbonyl groups of aldehydes, esters, and amides. Moreover, cycloadditions of Rh-carbenes and ring chain isomerizations will also be discussed in this section. 

Since the dipole moments of cyclopropenones are enlarged with respect to simple ketones and compare to other polar systems, e.g. trimethylamine oxide in Table 4, there seems to be evidence for considerable charge separation in the carbonyl group, which was expressed in terms of a cyclopropenium oxide contribution to the ground state. 

Typical reactions are amine or phosphine alkylation or addition to a carbonyl group (Scheme 3.3). In these examples, because of the development of dipoles in the TS, we are concerned with a polarity increase during the course of the reaction starting from the GS towards the TS. Favorable microwave effects are, consequently, expected. 

Carbonyl groups are very polar due to the high difference in the electron affinities of C and O atoms connected by the easily polarized Tr-bond. Aldehydes have high values of dipole moment (/r) [3]. 

Another factor that influences the reactivity of two polar reactants, acylperoxyl radical with aldehyde, is the polar interaction of carbonyl group with reaction center in the transition state. Aldehydes are polar compounds, their dipole moments are higher than 2.5 Debye (see Section 8.1.1). The dipole moment of the acylperoxyl radical is about 4 Debye (/jl = 3.87 Debye for PhC(0)00 according to the quantum-chemical calculation [54]). Due to this, one can expect a strong polar effect in the reaction of peroxyl radicals with aldehydes. The IPM helps to evaluate the increment Ain the activation energy Ee of the chosen reaction using experimental data [1], The results of Acalculation are presented in Table 8.10. 

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