Isomers structure

SUBSTITUTED BUTADIENES. The consequences of p-type orbitals rotations, become apparent when substituents are added. Many structural isomers of butadiene can be foiined (Structures VIII-XI), and the electrocylic ring-closure reaction to form cyclobutene can be phase inverting or preserving if the motion is conrotatory or disrotatory, respectively. The four cyclobutene structures XII-XV of cyclobutene may be formed by cyclization. Table I shows the different possibilities for the cyclization of the four isomers VIII-XI. These structmes are shown in Figure 35. 

Constitutional isomers are molecules with different connectivities between the atoms. Either the structures have different functional groups (these are called structural isomers), or the same functional group is placed in different positions (positional isomers). 

How many different structures (isomers) can you make that have the formula (a) CH2CI2 (b) Cl2C=CH2 and (c) C1CH=CHCU... 

Structural isomer (Section 1 8) Synonymous with constitu tional isomer... 

Table 3 shows the number of stmctural isomers possible when one, two, three, or four substituents, X, Y, and Z, replace the hydrogens of benzene. Table 3. Number of Structural Isomers of the Substitution Products of Benzene...

There are two possible structures (isomers) of three carbon atom alcohol. C is n-propyl alcohol (or 1-propanol), the other is isopropyl alcohol (or 2-propanol). The former, no.. ..mufaetured in large quantities is used in printing inks. The latter is manufactured in millions of tons to make propylene by a process similar to that used to convert ethylene to ethanol. The manutaclure of 2-propanol by this process initiated the petrochemical industry in the 1920s. 

PH3. Tetraphosphane(6), P4H6, exists as an equilibrium mixture of the two structural isomers H2PPHPHPH2 in) and P(PH2)3(i), and itself reacts with P3H5 at —20° according to the idealized stoichiometry P4H6 4- P3H5 ---> 2PH3 4-... 

Isomers are substances having the same molecular formula and molecular weight, but differing in physical and chemical properties. Since branched and straight-chain alkanes with the same molecular formula can exist as distinct structures having different geometrical arrangement of the atoms, they are termed structural isomers. One example is C H,j (butane) which has two isomers ... 

As the carbon number increases in the chain, the number of possible structural isomers grows very rapidly as a result of increased branching possibilities. For example, C H has only three isomers. 

The first three members of the olefin series are ethylene, propylene, and butylene (or butene). Structural isomers exist when n > 4, as a consequence of the positioning of the double bond in normal alkenes as a result of branching in branched alkenes. In addition, geometric isomers may be possible owing to restricted rotation of atoms about the C=C bond. For instance, C H (butene) has four possible isomers instead of the expected three ... 

Isomerism is commonly encountered in covalent compounds but is rare among ionic compounds. Isomers can be grouped under two major categories, namely structural isomers and. stereoisomers [48, p. 45]. 

Structural Isomers. These contain different combinations of bonded pairs of atoms. They may be divided into three types chain, position, and functional isomers,... 

Identification becomes more difficult in the case of isoparaffins since many structural isomers are possible with increasing carbon number. Nevertheless, all possible isoalkanes from through have been found in crude oils, along with several isomers of and some of Many isoprenoids (e.g., pristane and phytane) which serve as biomarkers to the genesis of petroleum have been detected in significant... 

Two pictures of two spatial (three-dimensional) models can represent the same structural formula without representing the same stereoformula they describe the same structural formula if they exhibit the same relationships (if they are topologically congruent, i.e., they satisfy conditions (I), (II), (III)). In order to describe the same stereoformula they must display the same relationships and the same spatial orientation [they satisfy (I), (II), (III), and in addition (IV) (with A ), that is, be spatially congruent]. If two formulas viewed as stereoformulas are equal then they are certainly equal when they are treated as structural formulas. Consequently there are at least as many stereoisomers as there are structural isomers. This fact is reflected by (2.8). It is true particularly for paraffins and monosubstituted paraffins. 

Multiply substituted paraffins. If there are more than three substitutions in a paraffin the generating function of the structural isomers becomes more involved. I will describe the construction but will forego the details of the proof. 

This illustrates an important distinction in chemical enumeration that between the enumeration of "structural" isomers, in which only the connections between the atoms are considered, and that of stereoisomers, in which the situation of a molecule in space is important, so that as above we can have right- and left-hand forms of a molecule. This distinction will occur, for example, when a carbon atom is bonded to four distinct substituents (it can occur in many other ways). Such a carbon atom is said to be asymmetrical. 

In the realm of chemical enumeration we note Polya s equation (4.4) which gives the generating function for stereoisomers of the alkyl radicals, or equivalently, alcohols — that is, equation (5.2) of this article. His equation (4.3) gives the corresponding result for the structural isomers of these compounds. His equations (4.2) and (4.5) correspond, respectively, to the cases of alcohols without any asymmetric carbon atoms and the number of embeddings in the plane of structural formulae for alcohols in general. The latter problem is not chemically very significant. 

Polya s Theorem clearly showed the way to the general enumeration of all acyclic hydrocarbons, irrespective of how many double or triple bonds they might have but it was to be 35 years before this enumeration was carried out. In two papers [ReaR72,76] I obtained the solution to this general problem in both the structural isomer and stereoisomer cases, as generating functions in three variables. Of these variables, x marks the number of carbon atoms, y the number of double bonds, and z the number of triple bonds. The de- rivation of these generating functions was Polya theory all the way — a succession of applications of Polya s Theorem with occasional use of Otter s result. The derivation was really rather tedious, but the generating functions, once obtained, can be used to compute the... 

AlsB77 Alspach, B., Aronoff, S. Enumeration of structural isomers in alicyclic hydrocarbons and porphyrins. Canad. J. Chem. 55 (1977) 2773-2777. 

BlaC34 Blair, C. M., Henze, H. R. The number of structural isomers of the more important types of aliphatic compounds. J. Amer. Chem. Soc. 56 (1934) 157. 

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