Hydrocarbons geometric isomers

Hydrocarbons Geometric isomers Functional group Amino acid... 

Butenes or butylenes are hydrocarbon alkenes that exist as four different isomers. Each isomer is a flammable gas at normal room temperature and one atmosphere pressure, but their boiling points indicate that butenes can be condensed at low ambient temperatures and/or increase pressure similar to propane and butane. The 2 designation in the names indicates the position of the double bond. The cis and trans labels indicate geometric isomerism. Geometric isomers are molecules that have similar atoms and bonds but different spatial arrangement of atoms. The structures indicate that three of the butenes are normal butenes, n-butenes, but that methylpropene is branched. Methylpropene is also called isobutene or isobutylene. Isobutenes are more reactive than n-butenes, and reaction mechanisms involving isobutenes differ from those of normal butenes. 

Polychlorinated hydrocarbons, such as polychlorinated dibenzodioxins, dibenzofurans, and biphenyls exist as a number of different congeners. Some of these are geometric isomers. Many cause a range of toxic effects that are believed to be mediated by interaction with the aryl hydrocarbon receptor (AhR) (they are known as pleiotropic effects). However, not all the isomers cause these effects because they do not all interact with the AhR receptor. To interact with this receptor, the molecule needs to be flat (planar). It can be seen in the diagram (Fig. 5.2)... 

In normal-phase chromatography, polar components are more strongly retained than nonpolar components. Thus, hydrocarbon carotenes elute quickly while xanthophylls are retained and separated. This approach provides a more complete separation of polar carotenoids and their geometric isomers. This protocol is useful to the analyst that is specifically interested in the xanthophyll fraction of a sample. 

Which of the two is the cis form and which the trans form has not been determined. A third cinnamic acid, viz., iso-cinnamic acid, is also known, but the constitution of it has not been established. Cinnamic acid is found in nature in the resin storax both as the free acid and as the cinnamic alcohol ester, styrin. It is also found in Peru and Tolu balsams as the free acid and as the benzyl alcohol ester, the benzoic acid ester of benzyl alcohol being present also. Thus benzyl alcohol, benzoic acid, cinnamic alcohol and cinnamic acid are all constituents of esters present in these plant resins. Allo-cinnamic acid, the geometric isomer, is obtained from coca leaves from which the alkaloid cocaine is also obtained (p. 896). When cinnamic acid is heated with lime it loses carbon dioxide and yields the unsaturated side-chain hydrocarbon st3rrene, or phenyl ethylene, CeHs—CH = CH2. On reduction it yields first cinnamic aldehyde, found in oil of cinnamon (p. 842) and then cinnamic alcohol. Both cinnamic acid and allo-cinnamic acid yield anhydrides. 

The alkanes, also called saturated hydrocarbons, have only single bonds. The bonds are described by sp hybridization of the carbon atoms. When the carbon atoms are not bonded in a linear sequence, cases can occur in which two molecules with the same formula can have different structures, called geometrical isomers, with quite distinct properties. 

There are three different structures for the hydrocarbon pentane, C5H12. These structures are called geometric isomers because each has a different shape. Draw electron dot diagrams for the three possibilities. You can substitute a dash, like the stick in the gmndrop models, to represent each pair of electrons. 

Diastereomers are also encountered in unsaturated acyclic compounds. When two C atoms are joined together by a double bond, all the remaining four single bonds to the two C atoms lie in the same plane as the C=C bond. If each of these two carbon atoms is bonded to a H atom and a hydrocarbon (alkyl) chain, the alkyl chains can be either on the same side of the C=C bond as each other or on opposite sides, and the resulting diastereomers (which used to be known as geometric isomers), shown in Fig. 2.2b, are termed cis and tram, respectively. Again, these diastereomers have different physical properties (see also Box 2.3). Optical isomerism is not possible about a C=C bond (the mirror images are superimposable). 

The chemistry or photochemistry of BQDI 53 [l,4-benzoquinone-bis(alkyl or aryl)imine] or BQMI 57 [l,4-benzoquinone-4-(alkyl or aryl)imine] is characteristic of the cross-conjugated systems having exocyclic C=N- bonds [77, 78], Both QI exist in the form of syn and anti geometric isomers. Model experiments revealed that QI retard thermooxidation of hydrocarbons and polymers and photo-oxidation of hydrocarbons [3,4,58,75], They are weaker AO than the parent PD and their effect is more pronounced in unsaturated substrates. For example, the Bandrowski s base 79 has a good antioxidant activity in... 

Resolution problems in the GC analysis of FA esters prompted many investigators in the past to develop capillary techniques to search for more selective stationary phases, and ultimately, to combine both approaches whenever required. In fact, FA esters were among the first substances (beyond hydrocarbons) that were successfully chromatographed on stainless steel capillary columns [355]. The most difficult separations involve different geometrical isomers, and the presence and positions of unsaturated carbon-carbon bonds. Such separations are non-trivial and justify the effort of numerous laboratories to solve these problems. 

Oxidation of Alkenes and Other Unsaturated Hydrocarbons. The epoxidation of double bonds has been the major area for the application of DDO methodology and a wide range of alkenes are effectively converted to epoxides by solutions of DDO. Epoxidation is stereospecific with retention of afkene stereochemistry, as shown by the reactions of geometrical isomers for example, ( -1-phenylpropene gives the cw-epoxide cleanly (eq 2), whereas the (E) isomer yields the corresponding trans-epoxide. Rate studies indicate that this reagent is electrophilic in nature and that alkyl substitution on the double bond enhances reactivity Interestingly, cw-disubstituted alkenes react 7-9 times faster than the trans isomers, an observation that has been interpreted in terms of a spiro transition state. ... 

Draw all the structural and geometric isomers of pentene, CjHjo, that have an unbranched hydrocarbon chain. 

Functional group (1.4) Geometric isomers (1.9) Homologous series (1.10) Hybrid orbital (1.3) Hydrocarbon (1.5) Hydrophobic (1.10) Inorganic chemistry (1.1) Isomerism (1.3)... 

Over 85% of the millions of known compounds are carbon compounds, and a separate branch of chemistry, organic chemistry, is devoted to the study of them. Why are there so many organic compounds The discussion of hydrocarbons and their structural and geometric isomers in Chapter 12 indicates two reasons (1) the ability of many carbon atoms to be linked in sequence with stable carbon-carbon single, double, and triple bonds in a single molecule and (2) the occurrence of isomers. A third reason will be discussed further in this chapter the variety of functional groups that bond to carbon atoms. 

Next, we examine aliphatic hydrocarbons. First we study the nomenclature and reactions of alkanes. We examine the optical isomerism of substituted alkanes and also the properties of cycloalkanes. We then study unsaturated hydrocarbons, molecules that contain carbon-to-carbon double bonds and triple bonds. We focus on their nomenclature, properties, and geometric isomers. (24.2)... 

In most cases, the difference in retention times between two analytes is governed by differences in physical properties such as polarity. For example, a more polar analyte will have a higher affinity to reside in the mobile phase and, therefore, have a shorter retention time. However, many RPLC systems have the ability to separate analytes that have very similar chemical functionalities and physical properties, but differ only slightly in molecular shape. This ability, termed shape selectivity, is typically applied in the context of separating the geometric isomers of rigid molecules, such as polycyclic aromatic hydrocarbons (PAHs), among others. However, the separation of alkane isomers illustrated in Fig. 2 is also a form of shape selectivity. 

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