 In silico calculations show that it takes 95 to 250 kcal/mol (400 to 1,050 kJ/mol) for this process.One of the most highly strained fenestranes to have been isolated is a [4.4.4.5]fenestrane with bond angles at the central carbon atom of around 130° (based on X-ray crystallography), as compared to the 109.45° standard for tetrahedral atoms.The carbon–carbon bond-lengths deviate from those of normal alkanes as well.