Fig. 16. ¹³C containing products from the reaction between 4^Mes-13C and CO. Top, signals for 8. Bottom, signals for 2^Mes. Circles signify ¹²C products, triangles signify mixed ¹²C/¹³C and square signifies ¹³C products. Markers in green are for ketene (8) and markers in red are squaraine (2^Mes).