Constitutional isomers structure

Molecules of the same empirical formula are either identical or isomers. Isomers either differ in the connectivity of their constituent atoms—this then involves constitutional isomers (structural isomers)—or they do not differ in this way then they are stereoisomers. Stereoiso-... 

Stereochemistry is the study of the three-dimensional structure of molecules. No one can understand organic chemistry, biochemistry, or biology without using stereochemistry. Biological systems are exquisitely selective, and they often discriminate between molecules with subtle stereochemical differences. We have seen (Section 2-8) that isomers are grouped into two broad classes constitutional isomers and stereoisomers. Constitutional isomers (structural isomers) differ in their bonding sequence their atoms are connected differently. Stereoisomers have the same bonding sequence, but they differ in the orientation of their atoms in space. 

Constitutional isomers (structured isomers) have the same molecular formula but differ in the order in which their atoms are attached. 

The earlier sections have only considered the way atoms are bonded to each other in a molecule (topology) and how this is translated into a computer-readable form. Chemists define this arrangement of the bonds as the constitution of a molecule. The example in Figure 2-39, Section 2.5.2.1, shows that molecules with a given empirical formula, e.g., C H O, can have several different structures, which are called isomers [lOOj. Isomeric structures can be divided into constitutional isomers and stereoisomers (see Figure 2-67). 

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). 

Wnte structural formulas for all the constitutional isomers of molecular formula C3HgO that contain... 

From among the 18 constitutional isomers of CgHig wnte structural formulas and give the lUPAC names for those that are named as derivatives of... 

Determine whether the two structures in each of the following pairs represent constitutional isomers different conformations of the same compound or stereoisomers that cannot be inter converted by rotation about single bonds... 

Two constitutional isomers of molecular formula CgHi20 are formed in the following reac tion Ignoring stereochemistry suggest reasonable structures for these Diels-Alder adducts... 

Compounds like the two C4M [() molecules and the three C3I I 12 molecules, which have the same formula but different structures, are called isomers, from the Greek isos + meros, meaning "made of the same parts." Isomers are compounds that have the same numbers and kinds of atoms but differ in the way the atoms are arranged. Compounds like butane and isobutane, whose atoms are connected differently, are called constitutional isomers. We ll see shortly that other kinds of isomers are also possible, even among compounds whose atoms are connected in the same order. As Table 3.2 shows, the number of possible alkane isomers increases dramatically as the number of carbon atoms increases. 

Alkanes are a class of saturated hydrocarbons with the general formula C H2n. -2- They contain no functional groups, are relatively inert, and can be either straight-chain (normal) or branched. Alkanes are named by a series of IUPAC rules of nomenclature. Compounds that have the same chemical formula but different structures are called isomers. More specifically, compounds such as butane and isobutane, which differ in their connections between atoms, are called constitutional isomers. 

Note the difference between tautomers and resonance forms. Tautomers are constitutional isomers—different compounds with different structures—while resonance forms arc different representations of a single structure. Tautomers have their atoms arranged differently, while resonance forms differ only in the position of their electrons. Note also that tautomers are rapidly interconvertible. Thus, keto and enol isomers are tautomers, but aJkene isomers such as 1-butene and 2-butene are not, because they don t interconvert rapidly under normal circumstances. 

The cyclotetramerization of suitable monopyrroles is the most simple approach to prepare porphyrins and it has been used in the synthesis of numerous porphyrin structures. But this method can only be used satisfactorily if the pyrroles 1 and 2 bear identical /i-substituents (R = R), otherwise the cyclotetramerization leads to a statistical mixture of four possible constitutional isomers. 

Although one of the two building blocks has to be symmetric to avoid constitutional isomers, the symmetry constraints differ from those of the 2 + 2 approach and this allows the synthesis of structures that would be difficult to obtain by other synthetic strategies. Consequently, the 3 + 1 strategy has been accepted and is an increasingly used method for porphyrin synthesis.49... 

Further heating of 36 at 110°C liberated N2 and gave the heterocyclopropane 37, which finally gave the unusual constitutional isomer 38 in quantitative yield (Scheme 8).38 The structure of 38 was also established by X-ray diffraction analysis (Fig. 12). 

Seebach, D., Abele, S., Gademann, K., Guichard, G., Hintermann, T., Jaun, B., Matthews, J. L., and Schreiber, J. V. (1998). /32- and /3 -peptides with proteinaceous side chains Synthesis and solution structures of constitutional isomers, a novel helical secondary structure and the influence of solvation and hydrophobic interactions on folding. Helv. Chim. Acta 81, 932-982. 

Constitutional isomers have different connectivity and, therefore, must have different structural formulas. 

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