What Are Alkanes

Although the three-dimensional shapes of larger alkanes are more complex than those of methane and ethane, the four bonds about each carbon atom are still arranged in a tetrahedral manner, and all bond angles are still approximately 109.5°. 

The next members of the alkane family are propane, butane, and pentane. In the representations that follow, these hydrocarbons are drawn first as condensed structural formulas that show all carbons and hydrogens. They are then drawn in an even more 

We can write structural formulas for alkanes in still another abbreviated form. The structural formula of pentane, for example, contains three CHg (methylene) groups in the middle of the chain. We can collect these groups together and write the structural formula as CH3(CH2)sCH3. Table 3.1 gives the names and molecular formulas of the first 20 alkanes. Note that the names of all these alkanes end in -ane. We will have more to say about naming alkanes in Section 3.3. 

Because carbon requires four bonds to satisfy its valency, count the number of visible bonds to each carbon and then subtract this number from 4 to determine the number of hydrogens also bonded to that carbon (but not shown). 

1 visible bond to each of these carbons. Therefore, each is also bonded to 4 -1 = 3 hydrogens (not shown) 

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What are alkane substitution reactions Provide an example. 

What two stereoisomeric alkanes are formed in the catalytic ] hydrogenation of ( )-3-methyl-2-hexene What are the relative amounts of each J... 

What are the reasons for the observed reactivity order of alkane hydrogens toward radical chlorination A look at the bond dissociation energies given previously in Table 5.3 on page 156 hints at the answer. The data in Table 5.3 indicate that a tertiary C—H bond (390 kj/mol 93 kcal/mol) is weaker than a secondary C-H bond (401 kj/mol 96 kcal/mol), which is in turn weaker than a primary C H bond (420 kj/mol 100 kcal/mol). Since less energy is needed to break a tertiary C-H bond than to break a primary or secondary C-H bond, the resultant tertiary radical is more stable than a primary or secondary radical. 

Before proceeding further, it will be well to reiterate what an alkane is, lest you be confused as to the difference between alkanes and alkenes. Alkanes are compounds of carbon and hydrogen only, without double bonds, triple... 

PROBLEM 23.7 What are the IUPAC names of the following alkanes ... 

In what sense are alkanes saturated Why are alkenes more reactive than alkanes ... 

What are the two most important reactions of alkanes What kind of additional reaction is possible with alkenes What may the latter have to do with the toxicological chemistry of alkenes ... 

What are the differences between the multiple-bond compounds and the alkanes ... 

What are the names of the radicals formed when a hydrogen atom is removed from one end of each of the first four unbranched alkanes (See Table 20.1 if... 

What are the reasons for the observed reactivity order of alkane hydrogens toward radical chlorination A look at the bond dissociation energies given previously in Table 5.3 hint at the answer. The data in Table 5.3 indicate that a tertiary C—H bond 1390 kJ/mol (93 kcal moil>l is weaker than a... 

We know from Sections 1.7 and 1.8 that an sp -hybridized carbon atom has tetrahedral geometry and that the carbon-carbon bonds in alkanes result from a overlap of carbon sp orbitals. Let s now look into the three-dimensional consequences of such bonding. What are the spatial relationships between the hydrogens on one carbon and the hydrogens on a neighboring carbon We ll see in later chapters that an understanding of these spatial relationships is often crucial for understanding chemical behavior. 

Q4. In the presence of a catalyst such as Pt, addition of hydrogen to an alkene brings about reduction to an alkane. Hydrogen is adsorbed on to the surface of the catalyst, and is then added syn to the alkene in a reaction that proceeds via a four-centre transition slate 68 (cf. hydroboration, Section 4.8.2). What are the products of reduction of compounds 69 and 70 with H-,/Pt and are the products racemic or meso1 Also, what is the product from reduction of I with D-j/Pt, and is this compound racemic or mesa What is the configuration of C(2) in the product ... 

The following questions can in principle be addressed with spectroscopy (1) Zeolite synthesis what are the mechanisms of ZSM-5 synthesis and how do they influence the quality of the catalyst synthesized (2) Catalyst characterization what are the structure and composition of the zeolite, and what is the configuration of the active site for methanol conversion (3) How do methanol and dimethylether interact with the active sites i.e. what species are present in the catalyst in the initial stages of methanol conversion (4) What are the subsequent reaction pathways leading to the final alkane, alkene and aromatic products (5) What causes catalyst deactivation This question concerns both the temporary deactivation associated with coke formation, which can be reversed by oxidative regeneration, and the permanent deactivation which occurs after repeated deactivation-regeneration cycles. 

Figure 20.3 shows the structures of the hydrocarbons propane and butane. Alkanes that contain an unbranched chain of carbon atoms are often called straight-chain alkanes. Why is such an unbranched chain not really "straight" What are the bond angles between the carbon atoms in propane and butane ... 

What are structural isomers What is the smallest alkane that has a structural isomer Draw structures to illustrate the isomers. 

Therefore, the biomimetic approach, that is the aeation of chemical analogues of enzymes, seems to be especially promising in this respect. The aeation of chemical models of the enzymatic oxidation of alkanes and arenes makes it possible not only to understand its mechanisms better, but also to develop what are likely to be fundamentally new processes for the conversion of the hydrocarbon raw material. 

What is a hydrocarbon What is the difference between a saturated hydrocarbon and an unsaturated hydrocarbon Distinguish between normal and branched hydrocarbons. What is an alkane What is a cyclic alkane What are the two general formulas for alkanes What is the hybridization of carbon atoms in alkanes What are the bond angles in alkanes Why are cyclopropane and cyclobutane so reactive ... 

What is the thermal conductivity of silicon nanowires, n-alkane single molecules, carbon nanotubes, or thin films How does the conductivity depend on the nanowiie dimension, nanotube chirality, molecular length and temperature, or the film thickness and disorder More profoundly, what are the mechanisms of heat transfer at the nanoscale, in constrictions, at low tanperatures Recent experiments and theoretical studies have dononstrated that the thermal conductivity of nanolevel systems significantly differ from their macroscale analogs [1]. In macroscopic-continuum objects, heat flows diffusively, obeying the Fourier s law (1808) of heat conduction, J = -KVT, J is the current, K is the thermal conductivity and VT is the temperature gradient across the structure. It is however obvious that at small scales, when the phonon mean free path is of the order of the device dimension, distinct transport mechanisms dominate the dynamics. In this context, one would like to understand the violation of the Fourier s... 

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