⚗️ Sinolook Chemical · Electronic Chemicals

Cis vs Trans 1,2-Diaminocyclohexane: Isomers, Chirality & Stereoisomers Explained

🧬 cis · (1R,2R) · (1S,2S) - which isomer do you need?

Few details matter more when buying 1,2-diaminocyclohexane (DACH) than its stereochemistry. The molecule comes in three forms - a cis isomer and two trans enantiomers, (1R,2R) and (1S,2S) - and the one you choose can make or break an asymmetric synthesis. This guide explains the differences clearly, answers the common chirality questions, and helps you specify the right grade. 🧬

For the underlying geometry, see our structure, formula & NMR guide, or start with the DACH overview.

🧬 The Three Stereoisomers of 1,2-Diaminocyclohexane

Because each amine-bearing carbon is a stereocenter, DACH has three distinct stereoisomers. The commercial "mixed" product (CAS 694-83-7) typically contains all of them. ✅

Stereoisomer	CAS No.	Character
cis-DACH	1436-59-5	meso form - achiral
(1R,2R)-trans	20439-47-8	chiral enantiomer (R,R / "RR")
(1S,2S)-trans	21436-03-3	chiral enantiomer (S,S)
trans (racemic)	1121-22-8	1:1 mixture of (1R,2R) + (1S,2S)

⚖️ Cis vs Trans: What's the Difference?

The terms cis and trans describe how the two amine groups sit relative to the ring plane. In cis-DACH, both –NH₂ groups point to the same face; in trans-DACH, they point to opposite faces. This seemingly small change has a big consequence: 💡

🔹 cis-DACH is a meso compound - it has an internal mirror plane, so it is achiral despite having two stereocenters.

🔹 trans-DACH has no internal mirror plane, so it exists as two non-superimposable mirror images - the (1R,2R) and (1S,2S) enantiomers.

❔ Is Cis-1,2-Diaminocyclohexane Chiral?

No - cis-1,2-diaminocyclohexane is not chiral. It is a meso compound: although it contains two stereocenters, an internal mirror plane makes the molecule identical to its own mirror image. That is why only the trans form yields useful enantiomers for asymmetric catalysis. The cis isomer cannot be "resolved" into optically active halves because there are none. 🔬

🔠 What Do (1R,2R), RR & (1S,2S) Mean?

The labels (1R,2R) and (1S,2S) use the Cahn–Ingold–Prelog system to define the absolute configuration at each stereocenter. "RR" is simply shorthand for the (1R,2R) enantiomer. These two enantiomers are physically near-identical (same melting point, density, NMR) but rotate plane-polarized light in opposite directions and behave completely differently in a chiral environment. 🧪

In practice, the (1R,2R) enantiomer is the one most often specified for the salen-type ligands behind the Jacobsen catalyst - see DACH-derived chiral ligands.

🔀 From Racemic Trans to Single Enantiomers

The commercially common racemic trans material (CAS 1121-22-8) is a 1:1 blend of the two enantiomers. To obtain a single enantiomer, chemists perform a chiral resolution using tartaric acid, forming separable diastereomeric salts. The full procedure is covered in How to Resolve Trans-1,2-Diaminocyclohexane with Tartaric Acid. The chemistry is also well documented on PubChem.

🎯 Which Isomer Should You Order?

✅ Epoxy curing, chelation, general synthesis: the mixed-isomer DACH (CAS 694-83-7) is usually the cost-effective choice.

✅ Chiral ligand / asymmetric catalysis: specify the resolved trans enantiomer - (1R,2R) or (1S,2S) - for the configuration your reaction needs.

✅ Racemic trans backbone: CAS 1121-22-8 when you plan to resolve in-house.

When in doubt, tell your supplier the application and target configuration - it prevents costly mismatches. Sinolook can advise on the right grade for your process.

🧫 Need a Specific DACH Isomer?

Sinolook Chemical supplies mixed-isomer and trans 1,2-diaminocyclohexane with COA confirming isomer profile and purity. Tell us your application and we'll match the grade.

👉 View DACH Product & Specifications

❓ Frequently Asked Questions

🔹 Is cis-1,2-diaminocyclohexane chiral?

No. Cis-DACH is a meso compound with an internal mirror plane, so it is achiral and cannot be resolved into enantiomers.

🔹 What is the difference between cis and trans 1,2-diaminocyclohexane?

In the cis form both amine groups are on the same face of the ring (achiral, meso); in the trans form they are on opposite faces, giving two chiral enantiomers, (1R,2R) and (1S,2S).

🔹 What is the CAS number of trans-1,2-diaminocyclohexane?

The racemic trans form is CAS 1121-22-8. The single enantiomers are (1R,2R) CAS 20439-47-8 and (1S,2S) CAS 21436-03-3; the mixed-isomer product is CAS 694-83-7.

🔹 What does "RR" 1,2-diaminocyclohexane mean?

"RR" is shorthand for the (1R,2R) enantiomer of trans-DACH, a key chiral building block for salen ligands and the Jacobsen catalyst.