Chirality in 3D

Choose a group for each slot A–D and press Show. The ideal tetrahedron represents one carbon center with the achiral groups H, OH, CH₃ and COOH. Its coordinates are dimensionless, not measured bond lengths. Four different groups give a stereogenic center; repeated groups give no R/S designation in this model.

Priorities. For these four groups the order is OH > COOH > CH₃ > H. Directly attached O outranks C and H. The two C groups are compared at the next level: COOH gives (O,O,O), including the duplicate atom used for its C=O bond, while CH₃ gives (H,H,H). This is a fixed example of CIP reasoning, not a general CIP or molecule parser; isotopes, rings and further centers are outside its scope.

R and S. Look with priority 4 pointing away: clockwise 1→2→3 is R, counterclockwise is S. “4 away” rotates each view to put 4 behind and 1 above. The fourth group then projects onto the central carbon and may be hidden behind it; its label and coordinates remain available. The fixed geometric test is det(p₁−p₄, p₂−p₄, p₃−p₄): negative for R, positive for S in this coordinate convention.

Reflection and rotation. The mirror is exactly (x,y,z)→(−x,y,z), shown in its own view. The rotation buttons apply proper +30° rotations about the displayed coordinate axes to both views; they preserve R/S. Swapping B/C changes the group assignment and requires Show again. Reset view only restores the view; Reset clears the result and retains the choices.

Projection. Both views use the same orthographic scale. Filled wedges point toward you, dashed bonds away, and plain bonds lie in the screen plane. Depth controls which groups cover others. Labels may be offset using leader lines; atom positions are not shifted. The coordinate tables give the actual rotated x/y/z values. A–D are slot names; 1–4 are priorities, omitted when groups repeat. The displayed symbols represent groups, not all atoms of a molecular structure.

Within-page navigation retains the result and views; reload retains only the four choices. Sources: IUPAC Blue Book, P9, especially P92.1.1–P92.1.6, and the IUPAC R/S definition.