September 29, 2009
September 27, 2009
name them...
3,4,5-trimethyl nonane
cis-3,4-dimethyldec-3-ene
4-chloro-nonan-1-ol
hexan-3-one
octanoic acid
3-bromopentanal
3-hydroxy-2-methylheptanal
September 25, 2009
isomer numbers...
The number of structural isomers that can be produced rises rapidly with the number of carbon atoms.. for example, the alkane with 4 carbon atoms has 2 isomers; the one with 7 has 9 structures ...C 10 has 75...and C20... has 366319!
There's more to alkenes than meets the eye...
Alkenes undergo electrophilic addition reactions, but with certain alkenes the question of orientation of addition arises. With the reaction of propene with hydrogen bromide, what will be the major product since two possibilities exist: 1-bromopropane and 2-bromopropane.
Alkenes can be simply classified into symmetrical or non symmetrical. To differentiate these two you need to look at the "alkenic" carbon atoms..and check which atoms they are bonded to. If the are bonded to CC and HH; or CH and CC then the alkene is non symmetrical. If the alkenic atoms are bonded to CC and CC; or CH and CH; or HH and HH [ie ethene] then the alkene is symmetrical.
When then considering the orientation of addition of hydrgoen halides, remember the statement: " unto those that have shall more be given"..
in other words the hydrogen atom of the hydrogen halide will end up being bonded to the alkenic carbon atom that already has most hydrogen atoms.
electrophiles, nucleophiles...and more!
Organic reactions are often classified using two words: one identifying the type of REAGENT and the other the type of REACTION.
Nucleophiles are electron pair donors, which use that pair to form a new bond to the substrate. If you are into A2 chemistry and interested in transition metal complex ions [and let's face it they ARE pretty amazing!] then nucleophiles could be called LIGANDS for these function in the same way!
Electophiles are electron pair acceptors; they accept a pair of electrons FROM the substrate to form a new bond.
Free radicals are very reactive intermediates which carry a single unpaired electron.
Alkanes are boring. Their olde name of "paraffins" was much more apt since it is derived from some Latin: "parum affinis" meaning 'little affinity'. See the benefits of a classical education? Since they contain only C-C and C-H bonds that are scarcely polar, electrophiles and nucleophiles are denied access, so we are left with free radicals. Since the substrate is Saturated, only Substitution can take place. Remember that free radicals [as their name implies] have no manners, and will give mixtures of products and multiple substitution with limited control. Their reactions with haloalkanes also give HX (g).
Alkenes contain a weak pi bond and, being UNsaturated, will suffer ADDITION reactions. The two pi type electrons are readily accessible to electrophiles, hence electrophilic addition reactions are the norm for alkenes. Whatever else happens the double bond does NOT break, for if it did the molecule would fall into two pieces!
Having put a halogen atom into the molecule we have now activated the substrate in a different way. The saturated haloalkanes now contain a polar C-Hal bond that will be subject to nucleophilic attack on the positively charged Carbon atom. Their reactions will therefore typically be nucleophilic substitution. Remember that the length and therefore strength of the C-Hal bond dictates reactivity NOT polarity, so the most reactive is C-I although the most polar is C-Cl.
September 17, 2009
Exam dates...
...this focusses the mind...
F321 [UNIT 1] THURSDAY 14TH JANUARY 2010 , morning [9am]
F322 [UNIT 2] THURSDAY 14TH JANUARY 2010 , morning [9am]
September 16, 2009
printing stuff...
...if you want to print off any of the notes on sutsci, simply "click on" the date line for that article. This will cause it to pop up in its own window...and then you can print in the usual way.
Biologists get in on the act...!
This is a picture of a nutrient agar plate with an unidentified mould growing on it. The concentric rings are most unusual [apparently] and so are deemed worthy of inclusion on my site! Good ol' biology...
Titrations
The exercise of volumetric analysis, sometimes also referred to as titrimetric analysis, is a central feature of the AS Practical work The techniques involved can be mastered through practice. The notes below describe some of the main points...
In a titration, a fixed volume of one solution in a conical flask is reacted with a second solution drained into the first from a burette. The volume added from the burette to the "end point" is called the titre. Either solution can be the "standard" i.e. the one whose concentration is known, and calculations ensue to determine the concentration of the other. Any further mathematics will depend on the ingenuity of the examiner!
The fixed volume is dipensed using a pipette, frequently, though not exclusively, 25.0 cm3. Special safety fillers are available. The pipette must be rinsed with solution first, before it is used to measure out the volume for the titration. If the pipette is wet, the water inside it will dilute the solution causing the titre to be too small. After draining the measured volume into the conical flask, the final drop must be left in the pipette and not blown out. Allow the pipette to drain for at least 30s before moving it away from the flask.
The burette must also be rinsed with the appropriate solution. If this piece of apparatus is wet then the solution will again be diluted, but this time the titre will be too large. The jet at the end of the burette must be seen to be filled with solution before starting the titration. The funnel must be moved from the top of the burette since it may drip and cause errors in readings. The burette scale must be read to 0.05 cm3, and two titrations to within 0.20 cm3 are required before any confidence in the readings can be held. The burette must be clamped vertically over the flask, with its jet just below the rim to prevent any loss by splashing.
During the titration a jet of distilled water must be used to rinse round the inside of the flask. Many candidates worry that this will somehow affect the titration. It will! It will make it more accurate since the rinsing will ensure that all of the reagents are in the body of the flask reacting with each other.
As the solution is drained into the flask, the contents of the latter must be swirled gently to ensure rapid mixing and reaction. As the end point is appoarched the rate of addition is slowed and time allowed for each drop to react before adding another. remember that as the end point is apporached the amount of reagent left in the flask has become very small so that the reaction with the solution entering from the burette will be very slow.
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September 11, 2009
A2
If you were successful at AS and wish to carry forwards please enrol now at Sutton campus. Classes start w/b 21st but on Thursday evenings.
see you soon!