In the previous few posts, we discussed Newman projections, their use in illustrating and understanding the conformational analysis of open-chain and cyclic structures, such as chair conformations. This post is a summary of practice problems on Newman projections.
Convert the following bond-line structure to the Newman projection as seen from the indicated angle:
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Convert the following bond-line structure to the Newman projection as seen from the indicated angle:
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Convert the following bond-line structure to the Newman projection as seen from the indicated angle:
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Convert the following bond-line structure to the Newman projection as seen from the indicated angle:
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Convert the following bond-line Chair Conformation to the Newman projection as seen from the indicated angle:
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The following exercise is to practice converting Newman projections to bond line structures. Check this article for some illustrations and handy tricks.
Use the instructions on the picture to convert each of the following Newman projections to the corresponding bond-line structure:
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Use the instructions on the picture to convert each of the following Newman projections of cyclohexanes to the corresponding bond-line structure:
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Draw the Newman projection for both molecules as seen from the specified direction:
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Practice Problems on Conformational Analysis
Circle all the gauche interactions (if any) in each Newman projection:
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Determine the most stable Newman conformation:
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Label the torsional and steric strain in each Newman projection:
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For each pair, determine the conformation with higher energy and calculate their energy difference using Table 1.
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Draw the structure of 2-methylpentane and calculate the barrier to rotation looking through the C2-C3 bond.
Use the following energy values for the ethyl group:
Here is the bond-line structure of 2-methylpentane:
Now, in order to draw the Newman projection, you need to add the hydrogens on carbon number and draw the methyl as a wedge or dash line (does not matter which one you choose):
Draw the arrow indicating the viewing angle:
And this is what you should get for the Newman projection:
To calculate the barrier to rotation, you need to first determine the most and the least stable conformations, looking through the indicated bond.
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