Calculating angle strain in actual compounds

WebCSD Teaching Examples

CONFORMATIONS OF RINGS > STEPS REQUIRED > Calculating angle strain in actual compounds

Calculating angle strain in actual compounds

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So far we only have a predicted value of angle strain in planar rings. We need a measure of angle strain in actual compounds, so that we can compare this to the predicted values.

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The preferred angle in actual compounds can be determined, for an n-membered carbocyclic ring, by taking the average internal angle across a large number crystal structures. Angle strain can then be calculated as the difference between this average internal angle and the ideal sp3 angle of 109.5.

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Calculate, from crystal structure data, the actual angle strain in cyclohexane. For this task you are provided with 5 structures each containing a cyclohexane ring (refcodes: BAVLOZ, CAFROR, CCXAPT, CLCHTF and CYCHEX). To display a structure type it’s reference code (refcode) in the Entry box above the structure list on the left hand side of the WebCSD page:

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Complete the table below by measuring, for each structure, all six internal C-C-C angles, then calculate the average internal angle of that structure and the overall average across the set of 5.

To measure geometric parameters in the 3D viewer:

1. Select the type of measurment you wish to make by right-clicking within the 3D viewer and selecting Measure, followed by either Distances, Angles or Torsions

2. Geometrical measurements (intramolecular or intermolecular) can now be made by clicking on e.g., two atoms for a distance, three atoms for an angle or four atoms for a torsion angle.

3. To remove all geometrical measurements from the display right-click within the 3D viewer and select Measure, followed by either Clear distances, Clear angles or Clear torsions.

Refcode

Internal C-C-C Angles

Average Internal C-C-C Angle

BAVLOZ

Angle 1:

Angle 2:

Angle 3:

Angle 4:

Angle 5:

Angle 6:

CAFROR

Angle 1:

Angle 2:

Angle 3:

Angle 4:

Angle 5:

Angle 6:

CCXAPT

Angle 1:

Angle 2:

Angle 3:

Angle 4:

Angle 5:

Angle 6:

CLCHTF

Angle 1:

Angle 2:

Angle 3:

Angle 4:

Angle 5:

Angle 6:

CYCHEX

Angle 1:

Angle 2:

Angle 3:

Angle 4:

Angle 5:

Angle 6:

Average internal C-C-C angle over whole set:

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Note: For the purpose of this task only a small number of representative structures are provided. However, if you have full access to the Cambridge Structural Database (CSD) the average internal angle can be calculated across a large number of cyclohexane fragments (see SUPPLEMENTARY MATERIAL: DETERMINING THE PREFERRED INTERNAL BOND ANGLE IN CYCLOHEXANE USING THE FULL CSD).