Esters

Question: Work out the number of esters with the molecular formula C4H8O2. - passerby

My reply: Esters have the functional group R-O-CO-R'. My drawing out the compound and permutating the number of ways the functional group can fit into the compound, this is what I get.
By inserting the functional group between the 3rd and 4th carbon atom will yield the same structural formula as (1). Hence, there're only 2 different esters resulting from the C4H8O2 formula. ;)

Bromoethene vs Bromopropene

Question: Suggest an explanation for e unreactivity of Br in bromoethene as compared to 3-bromo-propene - passerby

My reply: Okay, firstly i would assume that you're asking about electrophilic addition for both reactions involving Bromine. Bromine as you know is an electrophile, which is also an electron withdrawing atom. Hence, Br in bromoethene will "spread" the electrons out from the electron rich C=C and stabilises bromoethene. In 3-bromopropene (i'm assuming it's 3-bromo-prop-1-ene), the Br atom is too far away from C=C and hence it does not really "spread" the electrons from the pi bond across the molecule. In this way, the C=C pi bond in 3-bromopropene will be more susceptible to a bromine attack compared to bromoethene.

Iodoform reactions

Question: Does ethanamide & ethanoic acid give positive iodoform test?




Ans:

Okay, i've drawn up the molecules you asked abt and the required structural units for a positive iodoform test. As you can see, both ethanoic acid and ethanamide DO NOT HAVE either of the 2 structural units in the red box. Therefore the iodoform test will present a negative result.