Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Dissolving Borax Glass

Name: Dushyant
Status: student
Grade: 9-12
Country: India
Date:  Fall 2011  

Question:
Why do cis isomers have lower melting points than their trans isomers?

Replies:
It is not an absolute rule. It's true much of the time because molecules with the trans arrangement about a double bond pack better. That makes the solid state more stable, requiring more energy to disrupt (melt).

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy University of Wyoming


This may not always be true, but it may be true for most cis/trans isomers. The reason would have to do with the ability of the structure to sustain the inter-particle attractions required for a solid to form. Understanding this requires an understanding of permanent and temporary dipole-dipole forces. See:

.

Ray Tedder


Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory