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 test

The iodoform test (or tri Iodomethane test) is used to identify the presence of 2 particular structural units:


1)RCH(OH)CH3

2)RCOCH3

*R denotes H, alkyl or aryl group


In positive tests, the reaction will produce a yellow precipitate of CHI3.

*Click on picture for a clearer and bigger view

Any compound which contains the above mentioned structural units will result in a positive iodoform test. Ethanol is the only first degree alcohol to give a positive iodoform test. The following are some alcohols which may produce reactions with tri-iodomethane.

The compounds which produced a positive reaction all have the specific functional group [RCH(OH)CH3] and the boxed R-group. Propan-2-ol is unable to give a positive reaction because it does not have a CH3.

Here are the some other compounds which may react with tri-iodomethane:

The compounds which produced a positive reaction all have the functional group [RCOCH3] and a respective R-group boxed in red.

To figure out whether a compound has a positive iodoform reaction, always look out for it's functional group : [RCH(OH)CH3] or [RCOCH3]. If the compound does not have the specific functional group, it simply does not give a positive iodoform test and hence the equations for the reaction is not applicable.

-adapted and extended with permission from http://learnsg.blogspot.com-

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.

Area/Volume Formulas

Ever thought of compiling what you've learnt into bite sized information but you're too busy or lazy to make your own copy? Fret not, for here comes the time-savers you need! While i have been preparing for my exams, i've conveniently made my own copies of notes for easier references. It has always been so tedious for me to grab a couple of books and leave it on my table. It makes everything so messy. Here's one of the 'summaries' i've made - this one on Areas and Volumes.

**click on image to enlarge**

(*included - cuboids, closed cylinder, prism, pyramid, cone, sphere, sector, hemisphere)