Syntin

Syntin is a hydrocarbon with the molecular formula C₁₀H₁₆ used as a rocket fuel. It is a mixture of four stereoisomers. It has a density of 0.851 g/mL, and a boiling point of 158 °C. Due to the presence of three strained cyclopropane rings, the molecule has a highly positive enthalpy of formation: Δ_fH°= 133 kJ/mol, bringing additional energy into the combustion process. It has advantages over the traditional hydrocarbon fuels, such as RP-1, due to higher density, lower viscosity and higher specific heat of oxidation.
Syntin was used in the Soviet Union and later Russia as fuel for the Soyuz-U2 rocket from 1982 until 1995.
It was first synthesized in the USSR in 1959 and brought to mass production in the 1970s. It was prepared in a multi-step synthetic process from easily obtained acetylcyclopropane :
After dissolution of the USSR, the production of this fuel was halted due to the expense of the synthesis. On September 3, 1995, Soyuz TM-22, the seventy-first and last Soyuz-U2 rocket launched, being the last rocket fueled with Syntin.

Stereoisomers

Syntin has two stereocenters at the central cyclopropane ring. Thus, four stereoisomers exist:
In practice, syntin is used as a racemic mixture.

A. P. Mesheheryakov, V. G. Glukhovtsev, A. D. Petrov, "Synthesis of 1-methyl-1,2-dicyclopropylcyclopropane", Doklady Akademii Nauk SSSR, 1960, 130, 779–81.
Yu. P. Semenov, B. A. Sokolov, S. P. Chernykh, A. A. Grigor'ev, O. M. Nefedov, N. N. Istomin, G. M. Shirshov, "Multiple strained-ring alkane as high-performance liquid rocket fuel", RU 2233385, C2 20040727.
T. Edwards, "Liquid Fuels and Propellants for Aerospace Propulsion: 1903-2003", Journal of Propulsion and Power, 2003, 19, 1089–1107.
V. Azov, D. Vorontsov, "The last battle of hydrocarbons?", Novosti Kosmonavtiki, 2008, 18, No. 2, 44–46.