Are thiophene rings and chains more easily deformed than those in polyphenylene, polyfuran and polypyrrole? The conformation has great influence on the conjugation length of the polymers and therefore on their optical and electronic properties. Data obtained from an extremely rare X-ray structure determination of an alpha, alpha'-conjugated oligothiophene is compared with that obtained from solution studies and both are discussed in light of MMP2 force-field calculations.