CHE 381 Organic Chemistry I Lab Worksheet #4, continued 4. On the basis of disti
ID: 560878 • Letter: C
Question
CHE 381 Organic Chemistry I Lab Worksheet #4, continued 4. On the basis of distillation information, an unknown compound is believed to be one of the following pentane (b.p. 36°C) 2-pentene (bp 36°C) 1-chloropropene (b.p. 37°C) 1-bromoethane (b.p. 38°c) 2-methyl-2-butene (b.p. 39°C) 1-pentyne (b.p. 40°C) dichloromethane (b.p. 40°c) 3,3-dimethyl-1-butene (b.p. 41°C) 1,3-pentadiene (b.p. 42°C) iodomethane (b.p. 43 C) Since the boiling points are rather close together such that distillation is not adequate to make a definitive identification of the unknown, further analyses revealed that the unknown reacted as follows: Decolorized a Br2/CCl4 solution .No precipitate was observed following the addition of AgNHs)OH Treatment with alcoholic AgNO; did not yield a precipitate Based on the above information what is (are) the identityties) of the unknown compound? Explain your reaso (laboratory tests) could be used to further identify the unknown compound. Explain th your selection. 3 points) ning. If you cannot make a definitive identification, indicate what other information e reasons for Page 3 of 6Explanation / Answer
Tests:
1) Decolorized a Br2/CCl4 solution: There is an unsaturation in the molecule. (all possibilities of alkane are ruled out: Pentane)
2) No precipitation with Ag(NH3)2OH : Tollens' reagent is used to test aldehyde and terminal alkyne. As it gives negative results means there is no aldehyde/alkyne present. Tollen's reagent (ammoniacal silver nitrate) reacts with terminal acetylenes to form the silver acetylide which precipitates out of solution. (Possibilities of 1-pentyne is ruled out)
3) No precipitation with alcoholic AgNO3: No halide present. (all possiblities of alkyl halides are ruled out: DCM, 1-chloropropane, 1-bromomethane, iodomethane).
Thus the possiblities are as follows, the confermetive tests are given below:
2-pentene: decolorization of KMnO4 gives confirmetive test of presence of alkene. It is difficult to distinguish between 2-pentene, 3,3-dimethyl-1-butene, 1-3 pentadiene, and 3-methyl-2-butene. As all of these are alkenes. It will be possible to distingush between them further chemical transformation such as hydroboration will result in to different alcohol. Or adding HCl at high temperature will result in to different alkyl halides. All these methodes are distructive chemical analysis. We can use non-distructive techniques such as NMR will also revile structures of unknow compound.