Organic+Chemistry+Discussion

Hi Chem-O students!

If you find that you've read all you can from your textbook about ring conformations and cyclohexanes, you may wish to try the following link. There are some nice animations that you can click on, and some practice problems to try too!

Ring Conformers [NOTE: you do not need to know everything written in this page, e.g. the part about the twistboat conformation, etc..., but it is a good assessment of your ability to understand further information on the topic :)]

(Ms Bobillier, 10/5/2010)

Last lesson, we had a look at the chair conformation of cyclohexane. In fact, there is another metastable conformation for cyclohexane, named the 'boat' conformation. If you have time, search for what the boat conformation looks like, and how stable it is as compared to the chair conformation.

A useful tool can be found at the following website: [|Cyclohexane conformations]

Any other interesting links? Please post them here!

(Ms Bobillier, 4/5/2010)

This week, you should be reading up on //isomerism in alkanes//, like structural isomerism. Here's a video that can be useful! (Ms Bobillier, 27/4/10)

media type="youtube" key="qOhEJK4Umds" height="385" width="480"

Can anyone explain exactly what a **__dative bond__** is and why it is formed? (Ms Bobillier, 9/04/10)

Webpage: [|Definition of dative bond]
 * __1. What is a dative bond?__ **

(What I understood from it) Hence, a dative bond is a covalent bond where the pair of electrons is provided by only one of the participating atoms.
 * A dative bond is formed only between atoms that will bond covalently to form molecules.
 * One of the bonding atom would provide the pair of electrons, hence is referred to as the ‘donor’.
 * The other bonding atom would only accept the electron pair without sharing its own, and thus is referred to as the ‘acceptor’.

// The group which presented on this topic last week has given us an example of dative bond in the formation of NH4+, // N à H, is formed between Nitrogen of NH3 and one Hydrogen atom. // source of image: // http://www.tutorvista.com/content/chemistry/chemistry-iii/chemical-bonding/dative-bond.php

__(Some explanation if you need)__

Initially, N forms covalent bonds with 3 hydrogen atoms to produce compound NH3. N now has 1 lone pair of electrons in its valence shell. Another H atom loses its 1valence electron as it is the less electronegative than N, and becomes positively charged +1. It then forms a dative bond with Nitrogen, accepting the 2 electrons from Nitrogen’s lone pair, to form the duplet structure. In this bond, Nitrogen donates 1 pair of electrons and receives none, while Hygrogen donates none and receives 1 pair of electrons. Hence, the bond formed between the ‘donor’ Nitrogen and ‘acceptor’ Hydrogen is a dative bond.


 * __2. Why are dative bonds formed? (very unsure)__ **

Dative bonds are formed between an atom that has a pair of electrons to donate i.e. lone pair(s), and another atom that has an incomplete valence shell. I think dative bonds are formed during reactions of the two above mentioned atoms, as the latter atom does not have sufficient valence electrons to share and form the “usual” covalent bonds in order to gain a stable duplet/ octet structure. Dative bonds thus occur such that all the atoms in the compound formed will have full valence shells.


 * note: pls edit mistakes found in this entry freely as you wish. If it is more appropriate to upload this on the discussion page, could someone kindly help me to do so as my computer has a stupid error with the (new post) page in the discussion board. Thank-you! ;]

Thank you for that answer (Michelle, right?)! It's a very comprehensive explanation of what a dative bond is. As to why and where it is likely to form, you have indeed identified one of the reasons (namely, to achieve octet/duplet in atoms that had a deficiency in electrons). But there are other instances where dative bonds have the tendency to form. Anyone else would like to add on to the post above? (Ms Bobillier, 10/04/2010)

Dative bonds can be found in simple molecules like carbon monoxide (CO) or the ammonium ion (NH4). Dative bonds are also formed by electron deficient compounds, such as beryllium chloride (BeCl2). The Beryllium atom in this compound tends to bind two additional chlorine atoms, in which every beryllium atom is bonded to four chlorine atoms, two with normal covalent bonding, and the other two with dative bonds. Dative bonding can also be found in coordination complexes involving metal ions, especially if they are transition metal ions. Substances in a solution will donate their free pairs of electrons to the metal ion. Dative bonds form and the resulting compound is called a coordination complex. The electron donors are called ligands. A common ligand is water, H2O, which will form coordination complexes with metal ions, like Cu2+, which will form [Cu(H2O)6]2+ in aqueous solution. Other common simple ligands are ammonia (NH3), fluoride ions (F-), chloride ions (Cl-) and cyanide ions (CN-).

Source: [|http://www.wovre.com/revision/chemistry-unit-1-3-structure-and-bonding/]

Great resource Shi Hui! I like how you summarized where dative bonds occur :) (Ms Bobillier, 13/04/2010)

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