Thursday, September 27, 2007

March to freedom?

Sign this petition

March to freedom?

Riot police attack monks

Why protest?

For those who are unfamiliar with the background behind the junta: they organised a election in the early 1990s, in which aung san suu ki won, but refused to recognise this...

Sadly this is not going to be enough. International pressure is necessary before the junta will get out. Sadly, few countries are willing to take the moral high ground (e.g. Singapore, as chair of ASEAN, should do something).


More info from economist.com

In the last pro-democracy protests on this scale, in 1988, it took several rounds of massacres before the demonstrations finally subsided, leaving the regime as strong as ever. By Thursday September 27th, with a crackdown under way, and the first deaths from clashes with security forces, it seemed hard to imagine that things would be very different this time.

Myanmar’s tragic recent history suggests that when an immovable junta meets unstoppable protests, much blood is spilled.

As in the past, the world’s initial response to the junta’s violence was marked by bickering and point-scoring. On September 27th, the United Nations Security Council met in response to pressure from the West for co-ordinated sanctions. But Russia and China argued that the unrest was an internal matter that should not be on the council’s agenda at all.

If any countries can sway the junta they are the regional ones: ASEAN, especially Thailand; India; and above all China. China has given the junta diplomatic support, helping for years to keep its behaviour off the agenda of the United Nations Security Council. But Myanmar is far from a client state.

As in 1988 and 1990 the Burmese people have shown they want to choose their own leaders. In the past they did not fully reckon on the ruthlessness of the people they were up against. One day, as with all tyrannies, Myanmar’s will fall. But much blood may flow before that day dawns.

Monday, September 24, 2007

NSC 2007

It's been a long journey. Haha... but well, we walked home today with the championship today and laptops in hand.

We were quite shocked to get 2 pts for MCQ... disagreed on the 2 qns we got wrong, then stone/stupid choose wrong. Could have gotten 6, well but the other schs got 2 too... For the 2nd round, it was quite freaky when they whisked us to NTU to meet the environment faculty pple... it was the same pple as the failed NTU-RI, they recognise us. RG got a 2 pt lead here. In the demo round, once we got 12 for demo ahahaha. So we were now 1 point ahead, plus the eureka.

Buzzer round as usual was the most exciting/stressful. The questions were not difficult, but it's a whole new ball game up there vs a no-stakes situation. Plus RG's reaction time very pro, it was down to speed for some of the easy questions. There was a point where i thought RG was going to win... but we caught up in the end.


Pic frm barry... will replace with a pic the journalist is supposed to send me

A big thank you to all those who have helped us... Mr Wee, Mrs Lim, Mrs Yau - for your guidance and encouragement. Science club pple and lab techs - for helping us in the demo, and sparring us. And all supporters. This wouldn't have been possible without u.

And well done to RG and SC too! You gals certainly gave us a tough fight.

To the science club sec 2s... the title has been RI's for 2 years now. It's yours to defend next year.

Thursday, September 13, 2007

Arenes, Electrophillic substitution, and directing effects

For the first time... a chem post! No i'm not mr lumpy
Same thing has been posted on RA chem blog (see my links)


What is an Arene?

The homologous series Arenes are compounds based on the benzene ring C6H6. This ring, and its stability confer distinctive properties to any molecule that contains it.

Arene bonding and structure

Given benzene’s formula, C6H6, one would expect three C=C double bonds and three C-C single bonds. Hence it can exist as either of 2 resonant forms (left and centre in the diagram below), depending on the position of the double bonds.


In actual fact it exists as a mixture of both – each carbon atom uses its 2s and two of its 2p orbitals to form the σ framework of the benzene molecule (bonding to each adjacent C or H atom). The remaining 2p orbitals combine to form delocalised π orbitals, shared equally by each carbon atom (hence each bond is neither a single nor a double bond, but something in between), emphasized by the diagram on the right. Hence all carbon-carbon bond lengths in benzene are the same (0.139nm).

Delocalisation lowers the energy of the structure significantly (this is known as the delocalization enthalpy, about 150 kJ/mol). This electronic configuration and stability has a dominant influence on the properties of benzene.

For instance, even though benzene is unsaturated, it does not decolourise bromine water (the usual test for unsaturation). It does not readily undergo halogenation (common for alkenes) because addition of halides would destroy the delocalised π cloud.

Electrophillic substitution

As you read through this section, pay special attention to the position of electrons, it is the principle concern affecting further substitution reactions.

The most important reaction of arenes is called electrophilic substitution: an atom or group of atoms (called electrophile) replaces a hydrogen atom of the benzene ring (i.e. positively charged ions attack the cloud of π electrons).

Thus:C6H6 + E+ (an electrophile) --> C6H5E + H+

The mechanism of electrophile attack starts with attack by an electrophilic cation (e.g. Cl+ after heterolytic cleavage of Cl2). A Wheland intemediate (extreme right in the figure below) forms, in which the positive charge is shared by the five other carbon atoms in the ring. To stabilise the ring further, the intermediate then loses a proton, hence the net result is not an addition but a substitution.



Activating and deactivating groups

Existing functional groups attached to arene rings have effects on further substitution reactions.

Activating groups make further reactions more likely and faster, while deactivating groups make further reactions less likely and slower. Thus whether C6H5E would react faster or slower with another electrophile (say E’) will depend on whether E is an activating or deactivating group.

The first mechanism holds that activating groups must donate electrons to the arene ring (hence positively-charged electrophiles are now more attracted to the ring, relative to the hydrogen already attached to the ring), and deactivating groups withdraw electrons.

Alternatively, activating groups must stabilise the Wheland intemediate, hence lowering the activation energy and making the reaction more feasible.

Some activating groups

Halogen substituents such as Cl is more electronegative than benzene, hence withdrawing electrons and deactivating the ring.

A hydroxyl group (OH) is strongly activating. Oxygen (like carbon in the ring) has an filled but unbonded p orbital approximately perpendicular to the plane of the ring, hence when an OH group is attached to the benzene ring, the delocalised π electron cloud extends to this oxygen in the OH group.

Inductive effect: when electrophiles (positively charged functional groups) add to the arene molecule via electrophillic substitution, a cation (the wheland intemediate) is first formed (the electrophile attaches before the H breaks off). Usually the positive charge is stabilised by sharing this charge over all the C atoms. When the delocalisation is extended to the O atom, the positive charge can be shared by it as well, hence the positive charge on each atom is lessened, lowering the reaction's activationg energy (hence faster / more probable reaction). Hence we say that the OH group activates the ring.

The same inductive mechanism goes for methyl (CH3) or other alkyl groups, but these are less activating.

Some deactivating groups

Nitro (NO2) groups and ketone (COCH3) groups are deactivating because they withdraw electrons from the ring. The highly electronegative oxygen atom withdraws electrons from the atom substituting for hydrogen (i.e. N or C), such that delocalisation of electrons does not extend onto this atom, and electron density may be withdrawn from the ring.

Nitro groups are more deactivating than ketone groups, because of its 2 oxygen atoms (versus ketone’s 1), and because N is more electronegative than C, hence further withdrawing electron density from the ring

Directing effects

Activating groups are ortho and para directing (position 2, 4, and 6 on the ring), while deactivating groups are meta directing (position 3 and 5 on the ring).

Here's why. An incoming electrophile’s positive charge is concentrated on carbon 2, 4, 6 (where the original functional group is no. 1). If an electron donating group is already present in these positions, it will donate electron density, lessening the positive charge on and stabilizing this wheland intemediate. Hence the wheland intemediate leading to the 1,2 (ortho) and 1,4 (para) isomers have lower energy than the wheland intemediate leading to the 1,3 (meta) isomer, and therefore the ortho and para isomers are likely to form are therefore more likely to form.

Friday, September 07, 2007

Excerpts from Ecclesiastes (NIV)

My favourite verses:

2:10 I denied myself nothing my eyes desired; I refused my heart no pleasure. My heart took delight in all my work, and this was the reward for all my labour. 11 Yet when I surveyed all that my hands had done and what I had toiled to achieve, everything was meaningless, a chasing after the wind; nothing was gained under the sun.

3:16 ... there will be a time for every activity, a time for every deed.

4:6 Better one handful with tranquility than two handfuls with toil and chasing after the wind.

4:15 Naked a man comes from his mother's womb, and as he comes, so he departs. He takes nothing from his labour that he can carry in his hand. 16 ... As a man comes, so he departs, and what does he gain, since he toils for the wind? 17 All his days he eats in darkness, with great frustration, affliction, and anger.

8:7 Since no man knows the future, who can tell him what is to come? 8 No man has power over the wind to contain it; so no-one has power over the day of his death.

8:15 So I commend the enjoyment of life, because nothing is better for a man under the sun than to eat and drink and be glad. Then joy will accompany him in his work all the days of the life God has given him under the sun.

9:10 Whatever your hand finds to do, do it with all your might, for in the grave, where you are going, there is neither working nor planning nor knowledge nor wisdom

11:5 ... you cannot understand the work of God, the Maker of all things. 6 ... sow your seeds in the morning, and at evening let not your hands be idle.

11:9 Be happy, young man, while you are young, and let your heart give you joy in the days of your youth. Follow the ways of your heart and whatever your eyes see, but know that for all these things God will bring you to judgement. So then, banish anxiety from your heart and cast off the troubles from your body, for youth and vigour are meaningless.

12:13 Now all has been heard; here is the conclusion of the matter: Fear God and keep his commandments, for this is the whole duty of man. 14 For God will bring every deed into judgement.

Sunday, September 02, 2007

Phone cam pic spam #2

NSC:


Ahem... no wonder barry looks so tall on TV






Jerms.


Voodoo


3C before bio test: mugger's corner


Sunset at raja block

Mr Yuen's teacher's day gift from Geog RA: