Allotrope, of carbon

The NMR spectrum of SnMc4 consists of a singlet with two superimposed doublets. The coupling constants for the doublets are 52 and 54 Hz, and the overall live-line signal exhibits an approximately 4 4 84 4 4 pattern. Use data from Table 13.1 to interpret the spectrum. 

In Mc4Sn, all twelve protons are equivalent and one signal is expected. Sn has two NMR active nuclei Sn (7.6%, 7 = i) and Sn (8.6%, I = - The H nuclei couple to the Sn nucleus to give a doublet, and to the Sn nucleus to give another doublet. The relative intensities of the lines in the signal reflect the abundances of the spin-active nuclei  

6% of the H nuclei are in molecules containing and these protons give rise to a doublet. 

From the data given, it is not possible to assign these to 

The NMR spectrum of Me3SnCl contains five lines in a non-binomial pattern the separation between the outer lines is 372 Hz. Interpret these data. 

Although there are a number of compounds whose aqueous solutions are characterized by the formation of ions, this discussion will be limited to consideration of sodium carbonate (Na2C03). 

Dissolution of sodium carbonate generates sodium cations and the carbonate anion (Equation 1.12)  

We will assume that the state of hydration of the anion can be ignored and that, for the moment, the anion itself can be considered as an isolated system. In that 

The rules for writing valance bond descriptions of a species like the carbonate anion allow for understanding what constitutes a reasonable set of structures and, with discussion, follow  

The members of the set of structures have no individual reality. They are hypothetical representations of different electron-pairing schemes. 

The Sn nucleus is suitable for Mossbauer spectroscopy (see Section 4.10) and isomer shift values can be used to distinguish between Sn(ll) and Sn(IV) environments. The spectroscopic data may also provide information about the coordination number of the Sn centre. 

Apart from the chemical shift value, how do you expect well-resolved H NMR spectra of Me4Sn and Me4Si to differ  

The coupling constants for the doublets are 52 and 54 Hz. From the data given, it is not possible to assign these to coupling to a particular isotope. (In fact, 7( Sn- H) = 52 Hz, and7( Sn-H) = 54Hz.) 

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EttI R, Chao I, Diederich F and Whetten R L 1991 Isolation of C-g, a chiral (Dg) allotrope of carbon Nature 353... 

The eommonest erystalline forms of earbon, cubie diamond and hexagonal graphite, are elassical examples of allotropy that are found in every chemistry textbook. Both diamond and graphite also exist in two minor crystallographie forms hexagonal diamond and rhombohedral graphite. To these must be added earbynes and Fullerenes, both of which are crystalline earbon forms. Fullerenes are sometimes referred to as the third allotrope of carbon. However, sinee Fullerenes were diseovered more recently than earbynes, they are... 

Chapter 1 contains a review of carbon materials, and emphasizes the stmeture and chemical bonding in the various forms of carbon, including the foui" allotropes diamond, graphite, carbynes, and the fullerenes. In addition, amorphous carbon and diamond fihns, carbon nanoparticles, and engineered carbons are discussed. The most recently discovered allotrope of carbon, i.e., the fullerenes, along with carbon nanotubes, are more fully discussed in Chapter 2, where their structure-property relations are reviewed in the context of advanced technologies for carbon based materials. The synthesis, structure, and properties of the fullerenes and... 

Quite apart from the fullerene cluster molecules, numerous other molecular allotropes of carbon, C , have been discovered in the gases formed by the laser vaporization/supersonic expansion of graphite. The products are detected by mass... 

Much current research is centering on polyynes—linear carbon chains of sp-hybridized carbon atoms. Polyynes with up to eight triple bonds have been detected in interstellar space, and evidence has been presented for the existence of carbyne, an allotrope of carbon consisting of repeating triple bonds in long chains of indefinite length. 

Allotrope One of two or more forms of an element in the same physical state. Graphite and diamond are allotropes of carbon 02 and 03 are allotropes of oxygen, 250... 

Buckminsterfullerene is an allotrope of carbon in which the carbon atoms form spheres of 60 atoms each (see Section 14.16). In the pure compound the spheres pack in a cubic close-packed array, (a) The length of a side of the face-centered cubic cell formed by buckminsterfullerene is 142 pm. Use this information to calculate the radius of the buckminsterfullerene molecule treated as a hard sphere, (b) The compound K3C60 is a superconductor at low temperatures. In this compound the K+ ions lie in holes in the C60 face-centered cubic lattice. Considering the radius of the K+ ion and assuming that the radius of Q,0 is the same as for the Cft0 molecule, predict in what type of holes the K ions lie (tetrahedral, octahedral, or both) and indicate what percentage of those holes are filled. 

Robert Curl, Richard Smalley, and Harold Kroto were awarded the Nobel prize in chemistry in 1996 for the discovery of the soccer-ball-shaped molecule C60. This fundamental molecule was the first of a new series of molecular allotropes of carbon. The enthalpy of combustion of C60 is —25 937 kj-mol, and its enthalpy of sublimation is +233 kj-mol There are 90 bonds in C60, of which 60 are single bonds and 30 are double bonds. Like benzene, C60 has... 

Solid carbon exists as graphite, diamond, and other phases such as the fullerenes, which have structures related to that of graphite. Graphite is the thermodynamically most stable of these allotropes under ordinary conditions. In this section, we see how the properties of the different allotropes of carbon are related to differences in bonding. 

Distinguish the allotropes of carbon by their structures and show how their structures affect their properties. 

The carbon-based nanofillers are mainly layered graphite, nanotube, and nanofibers. Graphite is an allotrope of carbon, the stmcture of which consists of graphene layers stacked along the c-axis in a staggered array [1], Figure 4.1 shows the layered structure of graphite flakes. 

Ceo and higher fullerenes are distinguished from other allotropes of carbon, diamond and graphite, in that they exist as discrete molecules. The spherical or ellipsoidal nature of the monotropes opens up the possibility of intriguing new areas of chemistry. Here we are only interested in the hydrogen (or muonium) adducts, although this study has important implications to the very vigorous and extensive research in fullerene chemistry. 

A number of chemical elements, mainly oxygen and carbon but also others, such as tin, phosphorus, and sulfur, occur naturally in more than one form. The various forms differ from one another in their physical properties and also, less frequently, in some of their chemical properties. The characteristic of some elements to exist in two or more modifications is known as allotropy, and the different modifications of each element are known as its allotropes. The phenomenon of allotropy is generally attributed to dissimilarities in the way the component atoms bond to each other in each allotrope either variation in the number of atoms bonded to form a molecule, as in the allotropes oxygen and ozone, or to differences in the crystal structure of solids such as graphite and diamond, the allotropes of carbon. 

The allotropy of carbon is due to variations in the crystal structure of the element. There are three allotropes of carbon graphite, diamond, and... 

Figure 15.1 Three major allotropes of carbon (1 to r) diamond, lonsdaleite, and graphite.

To conclude are diamonds forever No. They convert slowly into graphite, which is the stablest form of carbon. Graphite has the lowest energy for any of the allotropes of carbon, and will not convert to diamond without the addition of energy. 

Diamond and graphite are allotropes of carbon. The density of diamond is 3.5 g/cm3 and that of graphite is 2.2 g/cm3. Diamond is used to cut other hard materials such as glass because of its hardness. On the other hand, softer graphite is used in pencils. 

The limitations of the simple Zintl-Klemm concept can be illustrated by differences in the two [MT1] intermetallics (M = Na [79] and Cs [80]). Complete electron transfer from M to T1 leads to [ M TI, where the Tl anion with four valence electrons is isoelectronic with a neutral group 14 atom and four bonds and needed to attain the octet configuration. Hence, the Tl- anion should form structures similar to allotropes of carbon or heavier group 14 elements. Indeed, [NaTl] has a stuffed diamond structure [79] with internal Na and an anionic (Tl-) lattice similar to diamond. However, the Tl- anions in [CsTl] form tetragonally compressed octahedra [80] unlike any structures of the allotropes of carbon or its heavier congeners. 

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