Electrochemical reductive carbonization of poly(tetrafluoroethylene) with alkali metal (Li, Na, K) amalgams leads to a polymeric carbon with a partly carbynoid structure. Raman spectra measured in situ exhibited a strong line at around 2000 cm-1 which was interpreted as the C≡C-C stretching mode of a linear carbon chain with alternating carbon-carbon triple and single bonds (polyyne). The intensity and position of this line evidence an unusually high triple bond carbon content in our materials, which leads to relatively large conjugation lengths in the polyyne chains. The triple bond line shifts to higher wavenumbers with increasing laser energy; this can be elucidated in terms of the conjugation length model. A quantum chemical calculation for transition energies and matrix elements of oligoynes with different chain lengths is presented. In addition, the frequency of the Σg mode as a function of chain length is calculated. The conjugation lengths found correspond to 8–14 C atoms in the polyyne chain and increase with increasing atomic number of the alkali metal. The yield of polyyne and its stability against interchain cross-linking increase similarly. This supports our previous conclusions about the polyyne stability which were formulated on the basis of electronic conductivity and UV-vis spectra.