Negative polarization

FIGURE 4 3 Adipole-dipole attractive force Two molecules of a polar sub stance associate so that the positively polarized region of one and the negatively polarized region of the other attract each other... 

Induced dipole/induced dipole forces are the only intermolecular attractive forces available to nonpolar molecules such as alkanes In addition to these forces polar molecules engage m dipole-dipole and dipole/mduced dipole attractions The dipole-dipole attractive force is easiest to visualize and is illustrated m Figure 4 3 Two molecules of a polar substance experience a mutual attraction between the positively polarized region of one molecule and the negatively polarized region of the other As its name implies the dipole/induced dipole force combines features of both the induced dipole/mduced dipole and dipole-dipole attractive forces A polar region of one mole cule alters the electron distribution m a nonpolar region of another m a direction that produces an attractive force between them... 

Organohthium and organomagnesium compounds are stable species when prepared m suitable solvents such as diethyl ether They are strongly basic however and react instantly with proton donors even as weakly acidic as water and alcohols A proton is transferred from the hydroxyl group to the negatively polarized carbon of the organometallic compound to form a hydrocarbon... 

Overall the reaction is classified as an addition Water adds to the carbonyl group Hydrogen becomes bonded to the negatively polarized carbonyl oxygen hydroxyl to the positively polarized carbon... 

Section 17 2 The carbonyl carbon is sp hybridized and it and the atoms attached to It are coplanar Aldehydes and ketones are polar molecules Nucleophiles attack C=0 at carbon (positively polarized) and electrophiles especially protons attack oxygen (negatively polarized)... 

You have already had considerable experience with carbanionic compounds and their applications in synthetic organic chemistry The first was acetyhde ion m Chapter 9 followed m Chapter 14 by organometallic compounds—Grignard reagents for example—that act as sources of negatively polarized carbon In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic and that this property can be used to advantage as a method for carbon-carbon bond formation... 

Based on gases at atmospheric pressure, 38°C, containing water vapor, air, CO2, and mist, using negative polarity electrical discharge. Recalculated from data reported in reference 176. 

Grown Macroring Inclusion Compounds (Coronates). Prototypical crown macrorings are cycHc ohgoethers such as given by formulae (1—4) (Fig. 3). Inside the hng they make available a negatively polarized cavity capable of accommodating metal ions to form crown cation inclusion... 

This means that the travelling wave will reflect in full but with negative polarity, thus nullifying the system voltage. The voltage of the refracted wave will also be zero, and obviously so, as there will be no refraction at the shorted end. Refer to Figure 18.10(b). 

A limited number of minus-x orientation samples were impact loaded in the vicinity of the Hugoniot elastic limit at stresses from 5.9 to 6.7 GPa. The principal observation of these experiments was that positive currents were observed from negative polarity disks when a stress of 5.9 GPa was exceeded. Such an observation confirms that quartz responds as predicted by the model, and that the elastic limit is in the vicinity of 6 GPa. 

There is a pronounced tendency for boron to become bonded to the less substituted carbon of the double bond. Thus, the hydrogen atoms of diborane add to C-2 of 1-decene, and boron to C-1. This is believed to be mainly a steric effect, but the regioselectivity of addition does conespond to Markovnikov s rule in the sense that hydrogen is the negatively polarized atom in a B—H bond and boron the positively polarized one. 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

Figure 17.1 Hydrogen-bonding in alcohols and phenols. A weak attraction between a positively polarized OH hydrogen and a negatively polarized oxygen holds molecules together. The electrostatic potential map of methanol shows the positively polarized O-H hydrogen (blue) and the negatively polarized oxygen (red).

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