scholarly journals Investigations of infra-red spectra. Determination of C-H frequencies (~3000 cm. -1 ) in paraffins and olefins, with some observations on “polythenes”

1940 ◽  
Vol 175 (961) ◽  
pp. 208-233 ◽  
Keyword(s):  
Double Bond ◽  
Carbon Tetrachloride ◽  
General Type ◽  
The Other ◽  
Hydrogen Atoms ◽  
Wave Numbers ◽  
Infra Red ◽  
Modes Of Vibration ◽  
Single Bonds

In a previous communication (1938) we described the results of an investigation into the infra-red absorption in the region of 3 µ of a number of hydrocarbons dissolved in carbon tetrachloride, with special reference to the absorption of ⟩CH 2 groups in different molecules. It was found that in many simple compounds the CH 2 group gave rise to two frequencies, essentially C-H valency vibrations, about 2857 and 2927 cm. -1 , and that from one compound to another these frequencies varied by only a few wave numbers. The lower frequency was identified with the mode of vibration in which the hydrogen atoms move in phase, while the other frequency was taken as the unsymmetrical mode of vibration. This assignment was substantiated by calculations with potential functions for molecules of the general type CH 2 — X , where X represents the rest of the molecule and is attached to the CH 2 group by single bonds. It was found that the CH frequencies of a CH 2 group are but little affected by the nature of X in saturated compounds, but that when the CH 2 group is attached to X by a double bond the CH frequencies are some 150 cm. -1 higher. In ethylene each CH 2 group has two CH valency modes of vibration, and since the CH 2 groups themselves can vibrate in or out of phase with one another, four CH frequency modes are possible for the C 2 H 4 molecule, two being Raman active and two infra-red active. In many molecules containing several CH 2 groups, similar coupling effects are important, and frequently four infra-red CH frequencies are observed.

Determination of Small Bone Particles in Meat

1968 ◽  
Vol 51 (6) ◽  
pp. 1175-1177 ◽  
Author(s):  
Robert M Hill ◽  
B D Hites
Keyword(s):  
Carbon Tetrachloride ◽  
Meat Products ◽  
The Other ◽  
Small Particles ◽  
Bone Content ◽  
Bone Particles ◽  
Small Bone ◽  
Good Agreement

Abstract Very small particles of bone can be separated from ground meats and meat products by the following procedure: The bulk of the meat is solubilized by digestion with papain and the bone is separated from the other nondigestible material according to its ability to settle in a carbon tetrachloride: acetone mixture. Turkey samples with widely varying bone content were analyzed, with good agreement between duplicate samples.

scholarly journals The normal vibrations of carbonate and nitrate ions

1931 ◽  
Vol 134 (823) ◽  
pp. 265-277 ◽  
Keyword(s):  
Raman Spectrum ◽  
Raman Spectra ◽  
Raman Effect ◽  
Normal Modes ◽  
Potassium Nitrate ◽  
Nitrate Ions ◽  
Carbonate Ion ◽  
Infra Red ◽  
Modes Of Vibration

When the Raman effect was first discovered, it was believed that every line in the Raman spectrum referred to some characteristic vibration of the scatter­ing molecule. Later the tendency was to regard the lines as due to transitions between states of vibration of the molecule, so that the energies corresponded not to energies of vibration directly, but to differences in the energy of vibra­tion of two different modes. It is now realised that the infra-red spectrum of a substance and the Raman spectrum which it scatters give complementary information. Certain modes of vibration are represented solely in the infra­red spectrum, others are found only in the Raman spectrum, while others may appear in both spectra. Quite early a rough criterion on the basis of symmetry was put forward by Schaefer, for the determination of whether or not a particular vibration was to be expected in the Raman effect. Recently a selection rule has been formulated by Placzek; no vibration will appear as a fundamental in the Raman effect if it is such that any symmetrical operation upon it can change the signs of the displacements of the normal co-ordinates, without altering the energy. It is clear that a knowledge of the normal modes of vibration of the molecule under discussion must precede the application of any such rule, and it is the purpose of the present communication to discuss the normal modes of vibration of the carbonate and nitrate ions. In 1929 the writer showed that it was possible to obtain Raman spectra from powdered crystals, and the discovery was made when using powdered crystals of potassium nitrate. The method was applied first to carbonates and nitrates, so it became of interest to attempt to fix the structure of the anions of these salts by means of the Raman spectra combined with the infra-red data. In what follows the carbonate ion will first be dealt with in some detail, and then the nitrate ion can be treated summarily owing to the similarity of structure of the two ions.

Sulfur Bond in Vulcanizates Implications of Halogen Reactions

1947 ◽  
Vol 20 (3) ◽  
pp. 627-648
Author(s):  
S. R. Olsen ◽  
C. M. Hull ◽  
Wesley G. France
Keyword(s):  
Double Bond ◽  
Carbon Tetrachloride ◽  
Sulfur Atom ◽  
Side Reactions ◽  
Double Bonds ◽  
Vulcanized Rubber ◽  
Iodine Chloride ◽  
Allyl Sulfide ◽  
Sulfur Bond

Abstract 1. When iodine chloride is used for the determination of double bonds in sulfur-vulcanized rubber or GR-S, it undergoes side reactions induced by combined sulfur. 2. Bromine in carbon tetrachloride is believed to give a satisfactory measure of the double bonds in a rubber-sulfur vulcanizate dissolved in dichlorobenzene-chloroform mixture. 3. The relation of one double bond consumed per sulfur atom combined in the rubber-sulfur type vulcanizate was confirmed. 4. Organic accelerators (in the absence of metal activators) catalyze the combination of sulfur without altering the ratio of one double bond loss per sulfur atom combined. 5. The introduction of a metal oxide or soap, such as zinc, causes a different type of vulcanization, which results in less than one double bond consumed per sulfur atom combined. 6. The reactions of propyl sulfide, dodecyl sulfide, propyl disulfide, allyl sulfide, methallyl sulfide, and butylmethallyl sulfide with iodine chloride and with bromine, respectively, are described. 7. The behavior of rubber-sulfur vulcanizates resembles that of butylmethallyl sulfide in reactions with iodine chloride and bromine, respectively; this suggests an alkyl-allyl type sulfur bond. 8. The theory of vulcanization proposed by Armstrong, Little, and Doak, based on the α-methylenic concept of Farmer, is supported by the findings of this investigation.

scholarly journals “Direct”, “Inverted” and “Superdirect” Sigma Bonds: Substituent Angles and Bond Energy. The Case of the CC Bonds in Hydrocarbons.

2020 ◽  
Author(s):  
Rubén Laplaza ◽  
Julia Contreras-García ◽  
Franck Fuster ◽  
François Volatron ◽  
Patrick Chaquin
Keyword(s):  
Dissociation Energy ◽  
Bond Energy ◽  
Multiple Bond ◽  
The Other ◽  
Hydrogen Atoms ◽  
The Mean ◽  
Sigma Bonds ◽  
Single Bonds ◽  
Sigma Bond

The A-A dissociation energy with respect to geometry frozen fragments (BE) of has been calculated for AHn-AHn models (C2H6, Si2H6, Ge2H6 and N2H4) as a function of  = H-A-A angles. Following a sigmoidal variation, BE decreases rapidly when  decreases to yield “inverted bonds” for  < 90° and finally nearly vanishes. On the contrary BE increases when  increases with respect to the equilibrium value; we propose the term of “superdirect” to qualify such bonds. This behaviour has been qualitatively interpreted in the case of C2H6 by the variation of the overlap of both s+p hybrids. The BE of one C-H bond in CH3 behaves similarly as function of its H-C-H angle with the other three hydrogen atoms. The concept of inverted/direct/superdirect bond is generalized to any CC sigma bond in hydrocarbons and can be characterized by the mean angle value <> of this bond with substituents (multiple-bonded substituents are considered as several substituents). This applies as well to formal single bonds as to sigma bonds in a formally multiple bond. <br>

Taking Away: Elimination

Reactions ◽  
2011 ◽  
Author(s):  
Peter Atkins
Keyword(s):  
Sulfuric Acid ◽  
Double Bond ◽  
Water Molecule ◽  
Natural Product ◽  
Triple Bond ◽  
Proton Donor ◽  
Electron Cloud ◽  
The Other ◽  
Single Bonds ◽  
Positively Charged

The hot spots of molecules that I have identified as double bonds (two shared pairs of electrons lying between the same two carbon atoms) and their triple bond cousins are often desirable entities. They are desirable either in their own right or because they can be used in the course of the construction of an elaborate molecule. For instance, a double bond can make the molecule stiffer and resistant to twisting. In Reaction 28 you will see that one particular natural product, quinine, must have a double bond in a particular position for it to be able to function—Nature is very particular about the shape of a molecule that she uses—and the drug’s synthesizers had to find a way to introduce it. How, though, can a double bond be introduced into a molecule that begins life with only single bonds? One approach is ‘elimination’, the expulsion of groups of atoms on neighbouring carbon atoms, leaving those two atoms free to form a second or even third bond to each other. One approach is to pull an H atom (as a proton) or some other group of atoms off one C atom, and then hope that the ensuing convulsions of the electron cloud will result in its accumulation to form a double bond between that C atom and its neighbour. There are two common approaches, one involving an acid and the other a base. Let’s watch what happens when sulfuric acid, 1, is added to 2. The acid, a proton donor, generates H3O+ ions in the usual way by transferring a proton to a neighbouring water molecule and leaving behind an HSO4– ion, and we see one of these ions sidle up to the target molecule. A proton hops across onto the O atom from the H3O+ ion, so forming a positively charged –OH2+ group. There is an immediate convulsion of the electron cloud, and that group escapes as an H2O molecule, leaving behind a positively charged ion with the positive charge mostly localised on the C atom. This ion is unstable but survives briefly.

DETERMINATION OF RELATIVE PORE SIZE IN LIVING MEMBRANES OF NITELLA BY THE TECHNIQUES OF ELECTROOSMOSIS AND RADIOACTIVE TRACERS

1967 ◽  
Vol 45 (8) ◽  
pp. 1267-1275 ◽  
Author(s):  
D. S. Fensom ◽  
D. J. Ursino ◽  
C. D. Nelson
Keyword(s):  
Carbon Tetrachloride ◽  
Pore Size ◽  
Indoleacetic Acid ◽  
The Other ◽  
Water Molecules ◽  
Radioactive Tracers ◽  
Before And After ◽  
Nitella Flexilis ◽  
In Cells

By measuring the number of water molecules per ion moved electroosmotically through living membranes of Nitella flexilis before and after the addition of chemicals to a solution of 10−4 M KCl, the effect of the chemical upon electroosmotic transport was investigated. Carbon tetrachloride and chloroform reduced slightly the amount of water transported per ion. On the other hand 10−5 M indoleacetic acid caused major changes in electroosmotic transport, increasing it in cells tested in July–August, but decreasing it in cells tested in October–November. Different ions also carry different amounts of water with them electroosmotically. These changes can be interpreted in terms of changing pore size.The relative pore size was also determined by measuring the permeation of glucose-14C and sucrose-14C in the absence and presence of electroosmotic transport and in cells treated with indoleacetic acid. Both the plasmalemma and tonoplast were freely permeable to glucose-14C but not to sucrose-14C. However, in the presence of electroosmotic transport sucrose did permeate the cell membrane. Indoleacetic acid enhanced this permeation of sucrose-14C.

Stringing Along: Radical Polymerization

Reactions ◽  
2011 ◽  
Author(s):  
Peter Atkins
Keyword(s):  
Double Bond ◽  
Radical Polymerization ◽  
Lower Energy ◽  
The Other ◽  
The Everyday ◽  
Radical Method ◽  
A Chain ◽  
First Time ◽  
Alternating Links ◽  
Single Bonds

Perhaps the most striking observable change brought about by chemistry as applied to the everyday world is in the texture of objects. Until the early twentieth century objects were manufactured from metal, wood, and animal and plant fibres. Today, synthetic polymers, in the vernacular ‘plastics’, are ubiquitous and have changed not only the appearance of the world but also its feel. Polymers (from the Greek words for ‘many parts’) are made by stringing together small molecules, the ‘monomers’, into long chains or extensive networks. Thus, polyethylene (less formally polythene) is a chain of linked ethylene molecules, and polystyrene is a chain of linked styrene molecules. In some instances, two or more different types of monomer molecules are used to form the polymer. Thus, one form of nylon is a chain in which the alternating links are of two different compounds. There are two main ways of linking molecules together, one involving radicals (Reaction 12) and the other not. In this section I shall introduce you to radical polymerization and treat the other kind in Reaction 14. Polyethylene and its cousins are made by the radical method, and I start with them. An ethylene molecule (1, formally, ethene) is written H2C=CH2, the double bar denoting a ‘double bond’. This is the first time I have needed to introduce you to a double bond, but it will turn out to be a crucial feature of all the monomers in this section. A double bond consists of two ordinary bonds linking the same two atoms. Because each bond consists of a shared pair of electrons acting as glue between two atoms, a double bond consists of two such pairs. Although a double bond between two C atoms is stronger than a single bond between C atoms, it is not twice as strong because the two pairs of electrons struggle for the best position and tend to push each other out of the ideal location for bonding. One consequence is that a molecule can acquire lower energy by giving up one of the pairs of electrons in the double bond and forming more single bonds with other atoms.

scholarly journals Vibration spectra of hydrocarbon molecules I. Frequencies due to deformation vibrations of hydrogen atoms attached to a double bond

1949 ◽  
Vol 196 (1045) ◽  
pp. 195-216 ◽  
Keyword(s):  
Double Bond ◽  
Theoretical Explanation ◽  
Force Constants ◽  
Hydrogen Atoms ◽  
Mean Values ◽  
Characteristic Frequencies ◽  
Alkyl Groups ◽  
Modes Of Vibration ◽  
The Mean ◽  
The Masses

An analysis has been made of the infra-red and Raman spectra of alkyl substituted ethylenes for ‘characteristic’ frequencies in the region between 1500 and 700 cm. -1 . The mean values of the frequencies characterizing the various types of substitution are as follows: asymmetrically disubstituted, 1415 and 890 cm. -1 ; trans -disubstituted, 1303 and 973 cm. -1 ; cis -disubstituted, 1260 and 973 cm. -1 ; mono-substituted, 1415, 1295, 990 and 910 cm. -1 ; trisubstituted, 1383 and 820 cm. -1 . These frequencies have all been assigned to specific modes of vibration, essentially localized in deformation motions of the hydrogen atoms directly attached to the double bond; the higher frequencies (>1000 cm. -1 ) are concerned with motions in the plane of the ethylenic double bond and the lower frequencies arise from motions out of that plane. Using a valency force field, a theoretical explanation has been given of the persistence of these characteristic frequencies in alkyl substituted ethylenes and detailed calculations have been made of the relevant force constants involved. The variation in certain of these characteristic frequencies when halogen atoms replace the alkyl groups has been considered and shown to be due to changes in the force constants and not to the changes in the masses of the substituents. For a given type of substitution, the force constant decreases progressively along the series alkyl group, iodine, bromine, chlorine and fluorine, i.e. with increasing electronegativity. The use of these methods to provide a means of following changes in the electronic structure of the double bond with substitution is discussed.

scholarly journals Investigations in the infra-red region of the spectrum. Part VI.—The absorption spectra of the dioxides of chlorine and sulphur

1932 ◽  
Vol 137 (833) ◽  
pp. 622-640 ◽  
Keyword(s):  
Band Spectrum ◽  
Absorption Tube ◽  
Electronic Band ◽  
Fundamental Frequencies ◽  
Infra Red ◽  
Modes Of Vibration ◽  
Glass Joint ◽  
Small Capacity ◽  
Universal Pattern

The infra-red spectrum of chlorine dioxide has not been previously determined, although its photochemical properties and its electronic band spectrum have been the subject of recent extensive enquiry. From the latter attempts have been made to interpret the band spectrum, and to assign values to the characteristic frequencies of the fundamental modes of vibration in the ground electronic state. It will be seen from the following that the values so deduced are incorrect, and it is probable that in no case of a polyatomic molecule is a complete determination of its fundamental frequencies possible without resort to its infra-red spectrum. Experimental . The method of preparation described by Goodeve and Stein ( loc. cit. ) was followed. The gas passed under water-pump vacuum to a trap immersed in a carbon dioxide-acetone freezing mixture; it was then distilled through phosphoric oxide tubes and condensed in a second trap cooled by liquid air. This trap could be removed from the generating system by means of a glass seal and a spherical glass joint; the ground joint was of universal pattern and the trap containing the dioxide could therefore be readily transported and connected to the absorption tube system. The latter was of as small capacity as possible, and no manometer was included, pressure in the absorption tube being regulated by immersing the dioxide trap in a freezing mixture of known temperature. The greatest pressure used during the investigation was the vapour pressure of the gas at 0° C., or approximately 630 mm. The length of the absorbing column of gas was in all cases 45 cm.; the lubrication of taps and of joints between the rocksalt end plates and the absorption tubes was effected by chlorinated vaseline.

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