Pick an alkene
Isomer:
Skeletal drawing (from the 3D model)
Assigning E or Z
Methyl groups are drawn with one C–H eclipsing the C=C bond, the preferred conformation in propene. With ideal 120° angles, cis methyls then collide (red H···H distance); a real (Z)-2-butene opens its C=C–C angles to about 127° to escape, which is part of why it is less stable than the E isomer.
Rank the two groups on each carbon separately (numbered badges: 1 = higher). Higher-priority groups on the same side → Z (zusammen); opposite sides → E (entgegen). The dihedral between the two priority-1 groups is measured in the model: 0° means Z, 180° means E.
honestmolecules.com · © 2026 Thomas R. Hoye and Daniel Lee. All rights reserved. Free for classroom and personal study with attribution; no redistribution, modification, or commercial use without written permission.
C H Cl Br
Click atoms to measure.