Sarahisme Posted June 12, 2005 Share Posted June 12, 2005 i can't see how these two molcules are the same....?? Link to comment Share on other sites More sharing options...
budullewraagh Posted June 12, 2005 Share Posted June 12, 2005 oh they look the same. AHAHAAHAHAH. but organic is soooo weird like that. these are enantiomers. while they appear to be the same, they are different. they rotate plane polarized light in opposite directions. it should be noted that they rotate light in equal amounts. in a given solution, if you have equal parts of an isomer that is optically active and its isomer, the solution is considered "racemic" and will not rotate the light. if you have unequal parts of chiral enantiomers of a compound, the solution is "scalemic." Link to comment Share on other sites More sharing options...
Sarahisme Posted June 12, 2005 Author Share Posted June 12, 2005 are you sure? because my answers booklet says that they are the same Link to comment Share on other sites More sharing options...
Sarahisme Posted June 12, 2005 Author Share Posted June 12, 2005 oh and while were on this topic, could you please please please (i have test tomorrow) explain how these bonds come to Z ? Thanks Link to comment Share on other sites More sharing options...
Sarahisme Posted June 12, 2005 Author Share Posted June 12, 2005 also how in world is this meso?! aghhh stress...!! Link to comment Share on other sites More sharing options...
woelen Posted June 12, 2005 Share Posted June 12, 2005 are you sure? because my answers booklet says that they are the same Indeed, they are the same, they are not enantiomers. The drawing of molecules like these in 2D is somewhat confusing. Imagine the right picture, and rotate the molecule, such that the H is pointing upwards. Then you have CH3 coming out of the plane, towards you, Br in the plane and NH2 going out of the plane, pointed away from you. This is the same situation as in the left picture. Link to comment Share on other sites More sharing options...
woelen Posted June 12, 2005 Share Posted June 12, 2005 also how in world is this meso?! aghhh stress...!! I assume that this picture is 1,2-cyclohexane-diol (1,2-dihydroxy cyclohexane). In this molecule, the bonds between the C-atoms are single. This means that the two items, connected at the C-atoms are pointing downwards and pointing upwards. So, you can have that both OH-groups are pointing upwards (relative to the plane, in which the 6-membered-C-ring is) or both of them are pointing downwards, or they point in opposite directions. Because the C-atoms are in a ring, there is no free rotational motion, so, a OH-group pointing downwards will remain so forever (assuming that the molecule as a whole is kept in the place and not rotated around an axis in the plane). In this way, just from plain 3D-geometry, you can easily see that a molecule is meso or not. In the picture you give, both OH-groups are pointing upwards. Link to comment Share on other sites More sharing options...
mezarashi Posted June 12, 2005 Share Posted June 12, 2005 Another of my cruddy paints Link to comment Share on other sites More sharing options...
Sarahisme Posted June 12, 2005 Author Share Posted June 12, 2005 I assume that this picture is 1,2-cyclohexane-diol (1,2-dihydroxy cyclohexane). In this molecule, the bonds between the C-atoms are single. This means that the two items, connected at the C-atoms are pointing downwards and pointing upwards. So, you can have that both OH-groups are pointing upwards (relative to the plane, in which the 6-membered-C-ring is) or both of them are pointing downwards, or they point in opposite directions. Because the C-atoms are in a ring, there is no free rotational motion, so, a OH-group pointing downwards will remain so forever (assuming that the molecule as a whole is kept in the place and not rotated around an axis in the plane). In this way, just from plain 3D-geometry, you can easily see that a molecule is meso or not. In the picture you give, both OH-groups are pointing upwards. so your saying that you could "move" the right hydrogen that is going into the page, so that it will point downwards, and so this would now look like it is 'mirroring' the left hand bit, hence making it meso ?? Link to comment Share on other sites More sharing options...
Bluenoise Posted June 13, 2005 Share Posted June 13, 2005 It's hard to see because of how it was drawn, visualizing the 3d representation in your head shows how it's meso. Here I've made a 3d render of it. Omiting unnecessary hydrogens. As you can see it's meso. It contains two chiral centre's but the molecule is actually achiral because of how their arranged. Link to comment Share on other sites More sharing options...
Sarahisme Posted June 13, 2005 Author Share Posted June 13, 2005 so was what i said correct? or way off track? :S Link to comment Share on other sites More sharing options...
Sarahisme Posted June 13, 2005 Author Share Posted June 13, 2005 *in my precious post Link to comment Share on other sites More sharing options...
Bluenoise Posted June 13, 2005 Share Posted June 13, 2005 Yeah you could redraw it and move the hydrogens to positions that make it easier to visulize if that helps, just don't flip them to the other face of the ring. But it's not necessary really. All you have to realize is that the hydrogens are on the same side of the plane of the molecule and the alcohol groups are on the other side of the plane. Link to comment Share on other sites More sharing options...
Crash Posted June 13, 2005 Share Posted June 13, 2005 Its Meso because even though it has chiral carbons it still has a plane of symmetry Link to comment Share on other sites More sharing options...
Sarahisme Posted June 14, 2005 Author Share Posted June 14, 2005 ok thanks everyone Link to comment Share on other sites More sharing options...
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