molecules that lack a permanent electric dipole moment and thus cannot be observed at these wavelengths. For cyanopolyynes, we study the emission of the radical CN, the cyanopolyynes HC$_3$N and HC$_5$N, and the related radical C$_3$N. We concentrated on these seven species because they display intense emission lines in the $\lambda~3$ mm spectrum of IRC+10216 and share a close chemical relationship as precursors or members of the family of acetylenic carbon chains.

An overview of the spatial distribution of C$_2$H, C$_4$H, and C$_6$H (left side) and CN, HC$_3$N, HC$_5$N, and C$_3$N (right side) is shown in Fig. \[fig:map\_all\], where we plot the brightness distribution of a representative line of each species, averaged over a velocity range of 3 km s$^{-1}$ centered at $V_{\rm LSR}=V_{\rm sys}$ (where $V_{\rm sys} = -26.5$ km s$^{-1}$ for IRC+10216; [@cer2000] 2000). The choice of this velocity range is very convenient for spherically expanding envelopes such as IRC+10216 because the maps show the brightness distribution in a plane perpendicular to the line of sight intersecting the star, allowing us to identify the radial dependence of the emission.

**C$_2$H and CN.** For the small radicals C$_2$H and CN, only the $N=1-0$ rotational transition of each falls within 