What is the longest unbranched alkane with a linear global minimum conformation?

Shea unbranched alkanes, such as heptane and hexane, prefer extended conformations. Polythene chains prefer folded conformations. How long a chain earn be built before the global minimum conformation ceases to be linear? The question is a difficult one, because exhaustive conformation searches on molecules of the size where the transition is likely to occur are very time consuming. This study demonstrates that the answer is not more than 17 for the MM2* force field and that the question provides a sensitive measure of comparison between force fields, solvent models, and semiempirical methods.