Syntin is a hydrocarbon with the molecular formula C10H16 used as a rocket fuel.

Due to the presence of three strained cyclopropane rings, the molecule has a highly positive enthalpy of formation: ΔfH°(l)= 133 kJ/mol (980 kJ/kg, the average value for the isomeric mixture),[1] 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 prepared in a multi-step synthetic process from easily obtained acetylcyclopropane (the 3rd molecule): After dissolution of the USSR, the production of this fuel was halted due to the expense of the synthesis.