Crystalline pentagonal nano- and microrods (PRs) and pentagonal nano- and microparticles (PPs) with 5-fold symmetry are studied. Structure of PRs and PPs and their elastic distortions are characterized in the framework of the disclination approach. Relaxation of mechanical stresses due to disclinations causes structural transformations in PRs and PPs. Experimental evidence of such transformations, namely, the appearance of internal cavities and pores, and growth of whiskers in copper PRs and PPs grown in the process of electrodeposition is demonstrated. A brief review of existing models of stress relaxation in PRs and PPs is presented. We discuss a new model of nanowhisker growth based on the nucleation of two dislocation loops of opposite signs near the surface of the crystal with disclination. As a result, vacancy-type dislocation loop remains in the material and serves as a nucleus for cavity, while the interstitial loop comes to the free surface and contributes to whisker growth.