“Curved arrows, the last in this series,
Address mechanistic-themed theories.
Show electrons’ movements
Through stepwise confluence;
Investigate synthetic queries.”
The 21 April 2023 Twitter limerick was the last to focus on a specific type of arrow used in chemical notation. It highlighted the curved arrows that are prevalent in organic chemistry mechanisms.
“Curved arrows, the last in this series, /
Address mechanistic-themed theories.”
Curved arrows are a convention used in organic chemistry to illustrate organic mechanisms: the depictions by which chemists map the theoretical step-by-step progress of multi-step chemical reactions. I had mentioned these in an earlier poem and post from this month’s endeavor, and that poem then inspired a more deliberate focus on such notation, over the course of an entire week.
“Show electrons’ movements /
Through stepwise confluence…”
Electron flow is the phenomenon that drives organic chemistry, as nucleophiles (electron-rich species) donate their electrons to electrophiles (electron-poor species). An organic mechanism is written as a series of steps in which electrons’ movements (more precisely, the movement of electron pairs) are illustrated, one step at a time.
“Investigate synthetic queries.”
Why are arrow-pushing mechanisms useful? They can allow organic chemists to ponder the feasibility of a particular “synthetic query,” better understanding why certain products form from certain reactants.
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A curved arrow is interpreted as showing the movement of the electron pair, which starts at the tail of the arrow and ends at the head of the arrow, in a given reaction step, as can be seen in some of the links from last year’s focus on mechanisms. Each “end of an arrow” has a specific meaning for an organic chemist, in terms of the curved-arrow notation.
Moreover, I simply could not avoid the pun (on “end of an era”) as a title here; as with the series of essays on enthalpy way back in 2020 or on kinetics in 2022, this was an undeniably dense set of posts. I’ll return to some less jargon-dependent rhymes in the weeks ahead!
Chemphasis 