[Gaz2.2]

Hi,

I haven't been well the past few days and only told today by a friend that we have to be able to discuss some sample questions we were given last week. Our performance in this will count towards 10% of our finals and i really need to do ok. If anybody can help me wiht any of the questions below, i will be very grateful, this is the one im stuck on at the moment:

"22. Describe, using hybrid molecular orbital theory, the bonding of carbon in methane and ethane."

Any help much appreciated!!!!

[Sam (NG)]

Do you mean hybrid molecular orbitals as in sp3 hybridised orbitals (valence bond theory)? Or do you mean molecular orbital theory?  In the case of VB theory, in both methane and ethane you would say that the carbon atoms were sp3 hybridised, meaning that each "hybrid orbital" is made from one s orbital and three p orbitals.

[Gaz2.2]

That's what i'm not too sure of myself. The question say's "using hybrid molecular orbital theory". I assume it would be the moleculae orbital theory?

Damn i'm so screwed, i need to have these prepared tomorrow, i have 6 but four i'm finding impossible. The above one and 3 others:

img108.imageshack.us/my.p...le1um1.jpg

img339.imageshack.us/my.p...le2rp7.jpg

img123.imageshack.us/my.p...le3br8.jpg

Thanks alot for the reply sam, means alot, i'm really stuck.

[Sam (NG)]

That's what i'm not too sure of myself. The question say's "using hybrid molecular orbital theory". I assume it would be the moleculae orbital theory?

Damn i'm so screwed, i need to have these prepared tomorrow, i have 6 but four i'm finding impossible. The above one and 3 others:

img108.imageshack.us/my.p...le1um1.jpg

img339.imageshack.us/my.p...le2rp7.jpg

img123.imageshack.us/my.p...le3br8.jpg

Thanks alot for the reply sam, means alot, i'm really stuck.

I can't see those images, you'll have to put image tags [ img ] [ /img ] around your image (without the spaces)

[Gaz2.2]

Sorry, this is them. Just click on the images. I never used the tags. I dunno if you know these sam, they are quite hard. And again thanks for the help, i kknow you probably have enough to worry about with your own course work!

[Gaz2.2]

Do they make any sense to yourself?

[Sam (NG)]

It states in the rules that we are ethically apposed to giving you the answers to questions, so unfortunately i can only guide you in the right direction.

From the level of these questions, i'm assuming that the other question was regarding the use of sp3 hybrids, and not molecular orbital theory.

2) Work out the length of the longest carbon chain, all other "side chains" to this chain are added as prefixes to the name e.g. ethyl, propyl.  I'm not sure what it means by "draw out the full structures", as far as i am concerned, they are the full structures, but i would think that they mean fill in the carbons and hydrogens for each structure, for example:



To identify cis or trans isomers use the following rule:

Largest groups on the same side - cis

Largest groups on apposing sides -trans

This only applies for alkenes with one hydrogen on each carbon.

3) E/Z notation.  Assign a priority to each group on the double bond based on the atomic number of the attached atom (1 highest priority).  If two attached atoms are the same, then look to the next atoms in each group to see whether the group is higher priority, for example -CH2OH is higher priority than -CH3.  If the two highest priorities are on the same side of the double bond then the isomer is Z (easy way to remember "Zame Zide", but actually stands for zusammen (german)), if they are on the opposite sides, then the isomer is E.

4) First reaction is Palladium Catalysed Hydrogenation, second is hydration of alkenes (see electrophilic addition to alkenes).

If you need something expanding, just ask.

[Gaz2.2]

I understand the whole answers thing. I will try work on your post and get them done tonight.

Thank you A LOT sam, really appreciate the help you have given this late!

[Gaz2.2]

Oh and just another thing, in relation to the first Q. Should i use the valance bond theory combined wiht sp3 orbitals and disregard the "use hybrid molecular oribital theory", or would that be wrong?

[Ψ×Ψ]

sp³ orbitals are hybrids.  Think about the C-H bond angles you'd expect to see with non-hybridized s and p orbitals as opposed to hybrid orbitals... 

[Sam (NG)]

sp³ orbitals are hybrids.  Think about the C-H bond angles you'd expect to see with non-hybridized s and p orbitals as opposed to hybrid orbitals... 

but this is different to the use of full molecular orbital theory, which is what i was saying.