Enter the Molecules

In his wonderful Lectures on Physics, Richard Feynman wrote If in a cataclysm 

1 UAU things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.  

It is therefore remarkable that 100 years or so before the laws of thermodynamics were formulated, Daniel Bernoulli developed a billiard ball model of a gas that gave a molecular interpretation to pressure and was later extended to give an understanding of temperature. This is truly a wonderful thing, because all it starts with is the assumption that the atoms or molecules of a gas can be treated as if they behave like perfectly elastic hard spheres—minute and perfect billiard balls. Then Newton s laws of motion are applied and all the gas laws follow, together with a molecular interpretation of temperature and absolute zero. You have no doubt 

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Compounds described as annnonolysed compounds, a term introduced by Franklin to indicate analogy to hydrolysis. For example, infusible precipitate, ClHgNII2, where ammonia has entered the molecule much as hydroxyl docs on hydrolysis. 

Addition reactions to the C = C bond arc observed in reactions of perchloryl fluoride in methanol in the presence of potassium carbonate at 15 C, when protected prostacyclins are fluorinated. Fluorine enters the molecule according to the Markovnikov rule and the formation of four isomers has been established.34... 

This one-to-one correlation of inversion with displacement must mean that the incoming iodide enters the molecule from the side of the substitution site opposite to the departing iodide every single time. It initially attacks the back lobe of the sp3 orbital used for bonding with the iodide. The transition state proposed by Hughes and co-workers is shown in 1. Carbon has rehybridized and is... 

If 3,4,5,6-tetrabenzoyl-D-glucose diethyl mercaptal is treated with ethanethiol and hydrochloric acid, a thioethyl substituent enters the molecule at carbon atom 2 and the product is 2-thioethyl-3,4,5,6-tetra-benzoyl-2-desoxy-D-hexose diethyl mercaptal192-196 (LXXI). This com-... 

It was pointed out in Section 4.2 that most polyatomic molecules show only a single relaxation process, owing to rapid intramolecular vibration-vibration transfer between modes. This corresponds to a state of affairs where Vibrational energy enters the molecule via process (a), which is rate-determining,... 

The model compound approach is also useful for studying reaction mechanisms. For example, as chlorine atoms in (NPC12)3 are replaced by OCH2CF3 groups, what is the pattern of halogen replacement Does the second fluoroalkoxy group enter the molecule at the same phosphorus atom as the first, or at an unsubstituted phosphorus atom... 

In the nitration of an aromatic compound, a N02 group enters the molecule (as NO 2f), and a hydrogen ion leaves. It is of interest to know whether the N0 ion pushes the hydrogen off in a single step, or whether the N02 group enters before H+ leaves (2-step mechanism) ... 

We are, of course, concerned with the symmetry aspects of the MOs and their construction. As was discussed before, the degeneracy of atomic orbitals is determined by mi. Thus, all p orbitals are threefold degenerate, and all d orbitals are fivefold degenerate. The spherical symmetry of the atomic subshells, however, necessarily changes when the atoms enter the molecule, since the symmetry of molecules is nonspherical. The degeneracy of atomic orbitals will, accordingly, decrease the extent of decrease will depend upon molecular symmetry. 

The theory that sulphonation takes place before the nitration can be accomplished may be the key to the question as to why some mono- and dinitrotoluenes are easily nitrated, and some are difficultly nitrated. The sulphonic group follows the laws of orientation perhaps more closely than almost any other group, and this explains why (assuming the sulphonation theory) dilute nitric acid will not nitrate direct, but will merely replace a sulphonic group. Therefore, if the sulphonic group is not already in place, the nitro-group cannot enter the molecule. So, if the previous... 

A late transition state is expected for the first step of the reaction, since it leads to the formation of an unstable species. An experimental manifestation of this was observed by Hoz and Livneh in the acid-catalyzed addition of MeOH to 35. The reaction was found to be general acid-catalyzed with a Bronsted a value of 0.98. In the second step of the reaction, the cyclobutyl cation is trapped by a nucleophile which usually enters the molecule cis to the proton or to any other attacking electrophile. Since this phenomenon was observed with a variety of substituents at the bridgehead position as well as with a spectrum of electrophiles, a 1,3 steric hindrance to the approaching nucleophiles is not likely. An alternative explanation of this phenomenon is that the cyclobutyl cation is obtained in a bent structure with the equatorial side more exposed to nucleophilic attack. 

The distribution of the radioactivity was as anticipated C-atoms 2, 15, and 17 were active whereas C-atoms 3, 4, 5, 12, 13, and 14 were not. Lysine-2-i4C was incorporated via a symmetric intermediate. The incorporation of doubly tagged a- N-Iysine-2-i4C into sparteine showed that the radioactivity of the was increased almost exactly by a factor of three over that of the ingested amino acid. A primary decarboxylation is therefore probable and 3 moles of lysine enter the molecule, the nitrogen being incorporated. This is strictly analogous to the incorporation of the amino acids into nicotinic acid. 

Chiral cyanohydrins have been synthesized by a number of routes, which differ mainly in the form in which HCN enters the molecules and in the source of chirality. 

Similar treatment of oxygen-containing compounds, such as alcohols,203 aldehydes, acids, esters,197 ethers, and acetals, is almost always less successful than that of aliphatic hydrocarbons in most cases only chlorine, and no sulfur, enters the molecule. 

An inspection of the steps of the above derivation reveals what changes will be introduced by a modification in the form of the chemical equation. If the reaction were of a tjrpe where two atoms of the first species and one of the second entered the molecule, we should have for the balance-sheet of the total numbers of atoms... 

CH3CH2CH2CH2CH2CH3 = CH4+CH2 CHCH3CH3CH3, then it is obvious that a considerable amplitude of vibration in the link 1—2 is a necessary preliminary to the separation of the two carbon atoms. We wish to form some idea of the factors which determine the accumulation in this bond of energy entering the molecule in a random fashion. 

When cellulose, such as cotton fiber, is nitrated, between two and three nitrate groups enter the basic CjHioOj group causing between 11 and 14% nitrogen (N) to enter the molecule. The lowest nitration with 11 % N leads to products that are soluble in numerous solvents. As pyroxylin or collodion cotton, they are part of lacquers and plastics, the best-known being celluloid (Formula 149). Not suitable as a propellant, such material is sometimes of pyrotechnic interest as a binder or as a consumable structural component that requires very little oxygen for combustion. 

The biosynthesis of Lythraceae alkaloids is not well understood. Lysine serves as a precursor for part of the molecule all carbons except the carboxyl group of lysine are incorporated. Further, the lysine-derived portion enters the molecule via a symmetrical intermediate. Phenylalanine... 

Had the reaction occurred with retention, a frontside approach would have been demanded. The incoming nucleophile would have had to enter the molecule from the same side as the departing leaving group. The tetrahedral umbrella would have retained its configuration. This result is not observed (Fig. 7.17). 

Chlorobutyl rubber is prepared by chlorinating the regular butyl polymer under controlled conditions so that reaction is primarily by substitution and little of the unsaturation originally present in the macromolecule is lost. The chlorine is believed to enter the molecule at the highly reactive ally lie position, one carbon removed from a double bond. Approximately 1.2 wt % chlorine is present in the commercial grades of Exxon chlorobutyl. The chlorine... 

Fig. 7. From Beamer et al [83] Proposed scheme for the stereospecific hydrogenation catalyzed by palladium-on-poly-(L)-leucine (a) of a-Methylcinnamic acid (b) of a-acetamido-cinnamic acid. In both cases the hydrogen should be viewed as entering the molecule Cis and from the catalytic surface, i.e., the hydrogen attack is in a direction from out of the page and toward the side away from the viewer.

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