Conformation of pentane

Higher alkanes having unbranched carbon chains are like butane most stable m then-all anti conformations The energy difference between gauche and anti conformations is similar to that of butane and appreciable quantities of the gauche conformation are pres ent m liquid alkanes at 25°C In depicting the conformations of higher alkanes it is often more helpful to look at them from the side rather than end on as m a Newman projec tion Viewed from this perspective the most stable conformations of pentane and hexane... 

Draw the most stable conformation of pentane, usi ng wedges and dashes to represen t bonds coming out of the paper and going behind the paper, respectively. 

Figure 3.4. Pentane. The diagram shows the four minimum-energy conformations of pentane. The global minimum is on the far left. Reflection and rotation of some of these geometries worrld generate more structures, but nothing with a different energy. Pentane is a simple molecule. More complicated molecules have many more conformations. Bryostatin 2 and PM-toxin A have so many mirrimtrm-energy conformations that to list them all would be a major undertaking and would require a large library to store the result.

Figure 6.9. Top to bottom Two possible Jahn-Teller distorted geometries for the methane radical cation and calculated geometry for its energy minimum schematic representation of the SOMO for ethane radical cation SOMOs of three different propane radical cations observed by ESR the SOMO of butane radical cation and SOMOs for two conformers of pentane radical cation.

Among the most widespread classes of acyclic compounds to exhibit stereoelectronic control over conformation are acetals. Take the simple acetal of formaldehyde and methanol, for example what is its conformation An obvious suggestion is to draw it fully extended so that every group is fully anti-periplanar to every other—this would be the lowest-energy conformation of pentane, which you get if you just replace the Os with CH2S. 

Figure 8. Schematic representation of the SOMOs for two conformers of pentane radical cation.

Draw a conformation of pentane in Newman projection, sighting down the C2-C3 bond with the methyl and ethyl groups staggered but not in the anti conformation. 

Fig. 2.21. The conformation of pentane associated with a sequence trans-gauche -gauche -trans. A sharp fold with elevated energy is formed...

The following is a wedge-and-dash structure for the anti-gauche conformation of pentane. Notice that Cl and C4 are anti to each other (when looking down the C2-C3 bond), while C2 and C5 are gauche to each other (when looking down the C3-C4 bond). 

Draw Newman projections for the staggered and eclipsed conformations of pentane for rotation about the C2—C3 bond. Which conformation is lowest in energy ... 

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