Cyclopropyl carbinol
[CAS 2516-33-8]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Cyclic hydrocarbon
• Name: Cyclopropyl carbinol
• Synonyms: Cyclopropanemethanol; (Hydroxymethyl)cyclopropane; CPMO
• Molecular Formula: C₄H₈O
• Molecular Weight: 72.11
• CAS Registry Number: 2516-33-8
• EC Number: 219-735-5
• SMILES: C1CC1CO

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 0.911 g/mL (Expl.)
• Melting point: -60 °C (Expl.)
• Boiling point: 124.3 °C 760 mmHg (Calc.)^*, 124.1 - 125.1 °C (Expl.)
• Flash point: 35.0 °C (Calc.)^*, 35 °C (Expl.)
• Solubility: water: miscible (Expl.)
• Index of refraction: 1.471 (Calc.)^*, 1.431 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS07;GHS08 DangerGHS02
• Risk Statements: H226-H302-H314-H319-H361-H373
• Safety Statements: P203-P210-P233-P240-P241-P242-P243-P260-P264-P264+P265-P270-P280-P301+P317-P301+P330+P331-P302+P361+P354-P303+P361+P353-P304+P340-P305+P351+P338-P305+P354+P338-P316-P318-P319-P321-P330-P337+P317-P363-P370+P378-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	3	H226
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319
Reproductive toxicity	Repr.	2	H361
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Skin corrosion	Skin Corr.	1B	H314
Skin corrosion	Skin Corr.	1C	H314
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2A	H319
Flammable liquids	Flam. Liq.	2	H225

• Transport Information: UN 1987

chemBlink Chemical Story

Cyclopropyl carbinol, CAS 2516-33-8, is a small cyclopropane-containing alcohol used as an intermediate and building block in organic synthesis. It is also commonly known as cyclopropylmethanol or cyclopropanemethanol. Its molecular formula is C₄H₈O and its molecular weight is 72.11. Structurally, it consists of a cyclopropane ring attached to a hydroxymethyl group, C₃H₅-CH₂OH. Despite this apparent simplicity, compounds containing the cyclopropylcarbinyl framework have played an important role in understanding how bonding and molecular rearrangement occur in strained carbon systems.

Cyclopropane is the smallest saturated carbon ring. Its three carbon atoms form a triangle with internal angles close to 60°, far smaller than the approximately 109.5° geometry normally preferred by tetrahedral carbon. The ring therefore possesses substantial strain, and its carbon-carbon bonds have unusual orbital characteristics often described in terms of bent bonds. These properties make cyclopropane chemically different from an ordinary open-chain alkane.

Cyclopropyl carbinol adds another functional feature to this strained ring: a primary alcohol. The hydroxyl group provides a convenient point for oxidation, substitution, esterification, ether formation, and conversion into other functional groups. The molecule can therefore serve as a compact source of the cyclopropylmethyl fragment in synthetic chemistry.

The cyclopropylmethyl group is particularly valuable in medicinal chemistry. Cyclopropane can introduce three carbon atoms while occupying relatively little space and restricting conformational flexibility. For this reason, cyclopropyl-containing fragments are frequently incorporated into biologically active molecules when researchers want to modify molecular shape, hydrophobicity, metabolic behavior, or binding interactions without introducing a long flexible alkyl chain.

Cyclopropyl carbinol is also interesting for a deeper historical reason. The cyclopropylcarbinyl system became one of the classic subjects in physical organic chemistry because derivatives of this structure can undergo remarkably rapid rearrangements when a positively charged carbon center is generated next to the cyclopropane ring.

If the hydroxyl group is converted into a suitable leaving group and ionization occurs, the resulting species cannot always be represented adequately as a simple localized cyclopropyl-CH₂⁺ carbocation. The neighboring cyclopropane carbon-carbon bonds can interact strongly with the electron-deficient center. This produces a delocalized cationic system in which bonding extends across several carbon atoms.

This chemistry is commonly discussed in terms of cyclopropylcarbinyl, cyclobutyl, and homoallylic cations. These apparently different carbon frameworks can interconvert extremely rapidly. Consequently, reactions beginning with a cyclopropylcarbinyl derivative may produce products corresponding not only to direct substitution but also to ring expansion or ring opening.

The phenomenon provided important experimental evidence in the long-running study of nonclassical carbocations. A classical carbocation is usually drawn with the positive charge concentrated primarily on one carbon atom. In nonclassical descriptions, electron density from neighboring bonds participates in stabilizing the electron-deficient center, so the positive charge and bonding cannot be represented accurately by one conventional two-center bond structure.

Cyclopropane is unusually capable of this interaction because its bent carbon-carbon bonds have significant orbital character that can overlap with an adjacent empty orbital. The three-membered ring is therefore not simply a strained spectator. Under suitable conditions, its bonds actively participate in the developing cationic system.

This also explains a seemingly surprising relationship between three different structures. A cyclopropylcarbinyl compound contains a three-membered ring plus an external carbon. A cyclobutyl compound contains those same four carbons in a four-membered ring. A homoallylic structure contains an open chain with a double bond. Under carbocation-forming conditions, rearrangement can connect these structural possibilities.

The alcohol itself is much more stable than the highly reactive carbocations used to study these processes. Simply storing or handling cyclopropyl carbinol does not mean that it continuously rearranges among these structures. The unusual chemistry becomes important when appropriate reaction conditions transform the alcohol or related derivatives into reactive intermediates.

In routine synthesis, the hydroxymethyl group can be manipulated without necessarily destroying the cyclopropane ring. Oxidation can provide cyclopropanecarboxaldehyde or, under stronger conditions, further oxidized products. Conversion of the hydroxyl group into activated derivatives permits nucleophilic substitution and the introduction of the cyclopropylmethyl unit into larger molecules. Appropriate reaction design is important because conditions that favor strongly cationic intermediates can instead encourage rearrangement.

This contrast makes Cyclopropyl carbinol particularly instructive. Under one set of conditions, its cyclopropane ring is a stable structural fragment that can be carried intact into a larger molecule. Under another, the same ring can participate electronically and allow the carbon skeleton to reorganize.

The compound therefore connects practical synthetic chemistry with fundamental questions about chemical bonding. To a synthetic chemist, it is a useful four-carbon building block containing an alcohol. To a physical organic chemist, the cyclopropylcarbinyl framework belongs to a classic family of molecular systems that revealed how rapidly carbon skeletons can reorganize and how chemical bonds can stabilize positive charge through delocalization.

Few molecules demonstrate this contrast so economically. Cyclopropyl carbinol contains only four carbon atoms and one oxygen atom, yet its structure leads directly from everyday functional-group chemistry to some of the most important concepts in carbocation structure and rearrangement. It is a reminder that molecular complexity is not measured simply by the number of atoms in a formula.

References

1. NIST Chemistry WebBook. Cyclopropanemethanol, CAS 2516-33-8. Molecular formula C₄H₈O; molecular weight 72.106.

2. Roberts, J. D.; Mazur, R. H. (1951). "The Nature of the Intermediate in Carbonium Ion-Type Interconversion Reactions of Cyclobutyl, Cyclopropylcarbinyl and Homoallyl Derivatives." Journal of the American Chemical Society, 73, 2509-2520.

3. Olah, G. A.; Prakash, G. K. S.; Saunders, M. (1983). "The Cyclopropylcarbinyl-Cyclobutyl-Homoallyl Cation System." Accounts of Chemical Research. Studies of structure, bonding, and rearrangement in cyclopropylcarbinyl cations.

4. de Meijere, A. (1979). "Bonding Properties of Cyclopropane and Their Chemical Consequences." Angewandte Chemie International Edition, 18, 809-826.

5. Wiberg, K. B. Studies and reviews of cyclopropane bonding, strain, and reactivity in physical organic chemistry.