Re: ORGLIST: IR Problem

Date view Thread view Subject view Author view Attachment view

From: Jacob Zabicky (zabicky$##$bgumail.bgu.ac.il)
Date: Wed Feb 28 2001 - 04:59:50 EST


Hello Ashutosh,

The assignment you made leaves as only possibility CH2=CH-CH2-OH. This is
because placing the hydroxyl group on the double bond gives an unstable
enol that rearranges to either acetone or propanal, depending on the
position of the OH. However, it is doubtful that the stretching band of the
OH and the broadening effect of hydrogen bond wouldn.t be mentioned as an
important feature of the spectrum.

You are left therefore with an alternative assignment for a double bond,
namely, a carbonyl group, corresponding to either a ketone (acetone) or an
aldehyde (propanal). The high frequency bands you mentioned are in the
stretching and bending frequencies of the carbonyl group, while the lower
frquency band may correspond to a bending mode of a parafinic group. Please
chech, these statements with a table of assignments.

All the best,

Jacob

At 14:37 27/2/1, Ashutosh wrote:
>Hello
>there's a problem in IR spectroscopy i am finding confusing
>
>a compound shows IR bands at 1620, 990 and 910 reciprocal cm.
>its molecular formula is C3H6O
>find its structure
>
>now,
>the band at 1620 refers to alkene C=C
>the bands at 990 and 910 refer to monosubstituted ethylene.
>my problem is;where does the oxygen fit in?there is no C=O.so the closest
>bet is an ether.
>but ethers show C-O stretching frequency at 1000-1300 reciprocal cm.
>so what could be the structure?
>
>thanks
>Ashutosh
>
><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
><HTML><HEAD>
><META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
><META content="MSHTML 5.00.2614.3500" name=GENERATOR>
><STYLE></STYLE>
></HEAD>
><BODY bgColor=#ffffff>
><DIV><FONT face=Arial size=2>Hello</FONT></DIV>
><DIV><FONT face=Arial size=2>there's a problem in IR spectroscopy i am finding
>confusing</FONT></DIV>
><DIV>&nbsp;</DIV>
><DIV><FONT face=Arial size=2>a compound shows IR bands at 1620, 990 and 910
>reciprocal cm.</FONT></DIV>
><DIV><FONT face=Arial size=2>its molecular formula is C3H6O</FONT></DIV>
><DIV><FONT face=Arial size=2>find its structure</FONT></DIV>
><DIV>&nbsp;</DIV>
><DIV><FONT face=Arial size=2>now,</FONT></DIV>
><DIV><FONT face=Arial size=2>the band at 1620 refers to alkene C=C</FONT></DIV>
><DIV><FONT face=Arial size=2>the bands at 990 and 910 refer to monosubstituted
>ethylene.</FONT></DIV>
><DIV><FONT face=Arial size=2>my problem is;where does the oxygen fit
>in?there is
>no C=O.so the closest bet is an ether.</FONT></DIV>
><DIV><FONT face=Arial size=2>but ethers show C-O stretching frequency at
>1000-1300 reciprocal cm.</FONT></DIV>
><DIV><FONT face=Arial size=2>so what could be the structure?</FONT></DIV>
><DIV>&nbsp;</DIV>
><DIV><FONT face=Arial size=2>thanks</FONT></DIV>
><DIV><FONT face=Arial size=2>Ashutosh</FONT></DIV></BODY></HTML>


__________________

ORGLIST - Organic Chemistry Mailing List
Website / Archive / FAQ: http://www.orglist.net/
List coordinator: Joao Aires de Sousa (jas$##$mail.fct.unl.pt)




Date view Thread view Subject view Author view Attachment view

This archive was generated by hypermail 2.1.4 : Fri Sep 19 2003 - 12:16:28 EDT