April 03, 2023
I’ve got a lot of strain, but I’m stable.
What molecule am I?
Image of [1.1.1]Propellane 3D Image of [1.1.1]Propellane

[1.1.1]Propellane is the smallest tricyclic hydrocarbon and the smallest member of the propellane family, which contains molecules as large as [10.3.3]propellane1. Only small quantities have been made, and few of its physical properties have been measured. It is a volatile liquid whose boiling point has variously been predicted to be 48 or 70 °C; but the true value is probably lower than 48 °C, based on other C5 hydrocarbons.

Because of its compact structure—three cyclopropane rings that share a common C–C bond—[1.1.1]propellane is highly strained. The central carbon atoms have an inverted tetrahedral geometry, which causes the central C–C bond length to be an unusually long 160 pm. (A normal C–C bond length is ≈154 pm.). When heated to 114 °C, [1.1.1]propellane isomerizes to 3-methylenecyclobutene2.

In 1971, Marshall D. Newton* at Brookhaven National Laboratory (Upton, NY) and Jerome M. Schulman at the Polytechnic Institute of Brooklyn (NY) performed theoretical studies on the then-unknown [1.1.1]propellane. Among other values, they calculated the central C–C bond length (which turned out to be accurate) and the strain energy at 105 kcal/mol (which is still generally accepted).

In 1982, noted organic chemist Kenneth B. Wiberg* and Frederick H. Walker at Yale University (New Haven, CT) reported the synthesis of [1.1.1]propellane. Their procedure began with bicyclo[1.1.1]pentane-1,3-dicarboxylic acid3, which they converted to 1,3-dibromobicyclo[1.1.1]pentane4 via a Hunsdiecker reaction (bromination of the silver salt). The dibromo intermediate was treated with tert-butyllithium to remove the bromine atoms and create the central C–C bond.

Hazard information for [1.1.1]propellane has not been reported, although it is likely to have properties similar to those of other C5 hydrocarbons.

1. CAS Reg. No. 58602-52-1.
2. CAS Reg. No. 27538-13-2.
3. CAS Reg. No. 56842-95-6.
4. CAS Reg. No. 82783-71-9.

Molecules from the journals

The ugonstilbenes are three cyclized geranylstilbenes found in the rhizomes of Helminthostachys zeylanica, a fern native to southeastern Asia and Australia that has been used in traditional Chinese medicine. The compounds were isolated in 2003 by Chien-Chih Chen and co-workers at the National Research Institute of Chinese Medicine (Taipei, Taiwan).

This past January, Ming-Jaw Don and colleagues at the same institution and at Chinese Culture University (Taipei) reported the absolute configurations and total syntheses of ugonstilbenes A1, B2, and C3. They also evaluated the cytotoxicity of the compounds against four human cancer cell lines, including colon, breast, and large-cell lung cancers and a T lymphoblastoid line. All the ugonstilbenes were toxic to all of the cancer cells, but at higher doses than doxorubicin4, an established chemotherapy agent.

1. CAS Reg. No. 736144-40-4.
2. CAS Reg. No. 736144-41-5.
3. CAS Reg. No. 736144-42-6.
4. CAS Reg. No. 23214-92-8.

Molecules from the journals

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fast facts

CAS Reg. No. 35634-10-7
SciFinder nomenclature Tricyclo[,3]
Empirical formula C5H6
Molar mass 66.10 g/mol
Appearance Colorless liquid
Boiling point See text
Water solubility Slight

MOTW update

Methyl methacrylate1 (MMA) was the Molecule of the Week for August 27, 2018. It is an unsaturated ester that is used to make polymers that range from water-based latexes to clear plastics.

On March 24, 2023, MMA and two other latex monomers, butyl acrylate2 and ethyl acrylate3, were released into the Delaware River during a discharge from a polymer manufacturing plant in Bristol, PA. All three monomers are respiratory and dermal hazards. On March 26, authorities stated that the tap water in Philadelphia and surrounding southeastern Pennsylvania communities was safe to drink; but they advised residents to use bottled drinking water. The result was panic buying that left store shelves empty. As of this writing, Philadelphia tap water has not been shown to be contaminated.

1. CAS Reg. No. 80-62-6.
2. CAS Reg. No. 141-32-2.
3. CAS Reg. No. 140-88-5.

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