Boat conformation steric strain

There are many other nonplanar conformations of cyclohexane, one of which is the boat conformation. You can visualize the interconversion of a chair conformation to a boat conformation by twisting the ring as illustrated in Figure 3.9. A boat conformation is considerably less stable than a chair conformation. In a boat conformation, torsional strain is created by four sets of eclipsed hydrogen interactions, and steric strain is created by the one set of flagpole interactions. Steric strain (also called nonbonded interaction strain) results when nonbonded atoms separated by four or more bonds are forced abnormally close to each other—that is, when they are forced closer than their atomic (contact) radii allow. The difference in potential energy between chair and boat conformations is approximately 27 kj/mol (6.5 kcal/mol), which means that, at room temperature, approximately 99.99% of all cyclohexane molecules are in the chair conformation. 

Boat conformation (cyclohexane), steric strain in, 118 Boc (fcJrf-butox carbonyl amide). 

Another conformation of cyclohexane is the boat conformation. Here the H atoms on C2-C3 and C5-C6 are eclipsed, which results in an increased torsional strain. Also, the H atoms on Ci and C4 are close enough to produce steric strain. 

Boat conformation (Section 6.5) The boat-sliaped conformation of cyclohexane that lias no angle strain blit does have some steric strain and some torsional strain. 

The less stable puckered conformation of cyclohexane, with both parts puckered upward. The most stable boat is actually the twist boat (or simply twist) conformation. Twisting minimizes torsional strain and steric strain, (p. 113)... 

X-Ray study of two 5,6-dihydropyrrolo[, 2-d 1,2,4 triazocin-6-oncs 7 and 8 showed boat conformation of the triazocine ring. Pyrrole ring and triazocinone skeleton are not coplanar and bend to avoid steric strain <1999T13703>. 

In addition to the chair conformation of cycloliexane, a second arrangc-menl called the twist-boat conformation is also nearly free of angle strain. It does, however, have both steric strain and torsional strain and is about 23 kj/mol (5.5 kcal/mol) higlier in energy than the chair conformation. As a result, molecules adopt the twisl-boat geometry unty under special circumstances. 

The chair forms of cyclohexane are 7 kcal/mol more stable than the boat forms. The boat conformation is destabilized by torsional strain because the hydrogens on the four carbon atoms in the plane are eclipsed. Additionally, there is steric strain because two hydrogens at either end of the boat—the flagpole hydrogens—are forced close to each other, as shown in Figure 4.14. 

Boat conformation of cyclohexane (Section 4.12B) An unstable conformation adopted by cyclohexane that resembles a boat. The instability of the boat conformation results from torsional strain and steric strain. The boat conformation of cyclohexane is 7 kcal/mol less stable than the chair conformation. 

The boat conformation of cyclohexane. There is steric strain and torsionai strain in this conformation but no angle strain. 

Cyclohexane adopts the chair or boat conformations, which are both free of angle strain. However, the boat conformation is less stable because of steric strain between the C-l and C-4 (or flagstaff) hydrogens. The two chair forms can interconvert via the boat form in a process known as ring-flipping. 

Cyclohexane can also exist in a boat conformation, shown in Figure 2.9. Like the chair conformer, the boat conformer is free of angle strain. However, the boat conformer is not as stable as the chair conformer because some of the bonds in the boat conformer are eclipsed, giving it torsional strain. The boat conformer is further destabilized by the close proximity of the flagpole hydrogens (the hydrogens at the bow and stern of the boat), which causes steric strain. 

Conversion of (a) a chair conformation to (b) a boat conformation. In the boat conformation, there is torsional strain due to the four sets of eclipsed hydrogen interactions and steric strain due to the one set of flagpole interactions. A chair conformation is more stable than a boat conformation. 

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