Core shells of molecules are largely ignored in quantum mechanical calculations of organic compounds. A novel means of studying chemical bonding mechanisms using core molecular orbitals (MOs) of n-butane conformational isomers is presented in r-space and k-space. It is demonstrated that the central MOs are more sensitive to energetic properties in real space. In contrast, the terminal MO pair is more sensitive in reciprocal space, reflecting the fact that the equivalent core MOs caused by orbital energy degeneracy in r-space can be differentiated in k-space. This work provides a unique and novel channel to study isomerization and suggests that a comprehensive understanding of the bonding mechanisms of molecules can be better achieved using information from both r-space and k-space. (C) 2003 Elsevier B.V. All rights reserved.