Understanding Curly Arrows in Organic Chemistry: Protonation Mechanisms and Delocalization, Study notes of Chemistry

Download Understanding Curly Arrows in Organic Chemistry: Protonation Mechanisms and Delocalization and more Study notes Chemistry in PDF only on Docsity! How to use curly arrows: You should read each frame and answer the question while keeping the fol lowing frame covered. 1. The curly arrow which chemists use to draw mechanisms means: the movement of a pair of electrons from one end of the arrow to the other So, when ammonia is protonated, the arrow moves from the lone pair of electrons on the nitrogen atom into the gap between N and H to make a new N-H bond: H3N H H3N H The positive charge is now on nitrogen, because it has lost electrons. Draw the protonation of benzylamine, PhCH2NH2 *** 2. You should have drawn this: PhCH2NH2 H PhCH2NH2 H The oxygen atom has lone pairs too. Draw the protonation of ether, Et2O *** 3. Et2O H Et2O H Sometimes the arrow starts on a negative charge, since this is a lone pair of electrons which can form a bond. Hydroxide ion reacts with a proton like this: H HO HO H Draw the protonation of acetate ion, O O *** 4. H O O O O H We can use bonding electrons to form new bonds, as in the protonation of an olefin: H H H H H H H H H H Note that the arrow begins this time in the middle of the bond. Draw the protonation of cyclohexene. *** 5. H H These ions are very unstable and would in fact react further. Some ions are more stable because of delocalisation; this can also be represented by curly arrows: H H H H H H H H How would you show delocalisation in this ion: OH *** 6. OH OH These “reactions” do not produce new cations – they simply produce new ways of writing the old cation. The double-headed arrow indicates this. Delocalisation occurs in neutral molecules too: Show the delocalisation here: N O O ***