When considering molecular conformations, which of the following statements are true?

Question

BlackTom AI · Accepted Answer

Begin by examining what determines conformational changes in molecules. 
Option 1: 'Different conformations are generally reached by rotation about a C-C single bond, a low energy process.' This is correct because rotation around a C-C single bond typically has a small energy barrier (torsional barrier), allowing interconversion between conformations at moderate temperatures without breaking bonds. This is the classic mechanism for conformational changes in alkanes and many other molecules. 
Option 2: 'At room temperature conformations of ethane do not interchange.' This is incorrect; ethane readily undergoes torsional rotation about its C-C bond, leading to rapid interconversion of staggered and eclipsed conformations even at room temperature. 
Option 3: 'Different conformations are generally reached by rotation about a C-C single bond, a high energy process.' While rotation about a C-C single bond is indeed a rotation process, calling it high energy is inaccurate for many simple systems like ethane; the energy barrier is relatively low. The statement mischaracterizes the typical energy landscape of single-bond rotations. 
Option 4: 'Different conformations are generally reached by breaking and reforming C-C bonds.' This is wrong because conformational changes occur through bond rotations without breaking the bonds; breaking and reforming C-C bonds would constitute chemical reactions altering connectivity, not mere conformational interconversion. 
In summary, the only statement aligning with established understanding of conformational dynamics is Option 1, as it correctly identifies rotation about C-C single bonds as the low-energy mechanism driving interconversion between conformers.

CHM1052 - MUM S2 2025 CHM1052 2022 practice exam 1

When considering molecular conformations, which of the following statements are true?

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