  The transmission of a vertex $v$ of a (chemical) graph $G$ is the sum of
distances from $v$ to other vertices in $G$. If any two vertices of $G$ have
different transmissions, then $G$ is a transmission irregular graph. It is
shown that for any odd number $n\geq 7$ there exists a transmission irregular
chemical tree of order $n$. A construction is provided which generates new
transmission irregular (chemical) trees. Two additional families of chemical
graphs are characterized by property of transmission irregularity and two
sufficient condition provided which guarantee that the transmission
irregularity is preserved upon adding a new edge.
