Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: omid on 10/06/2009 18:37:53
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how does ethane undergo free redical substitution ander high energy conditions?
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What do you know about radical substitution reactions?
Do you know about halogenations for example. These people can draw better pictures than I can.
http://en.wikipedia.org/wiki/Free_radical_halogenation
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What don't you get?
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i didnt get if free redical substitution and helogenations is the same.
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Halogenation is just the addition of a halogen(s).
Free radical substitution can be any radical, for example a methyl radical CH3•
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i got you SIR but can you please tell me that for my task they are asking free redical substitution so i dont need to add helogenation right?
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Free radical substitution can include halogenation, like in that link Bored Chemist gave you.
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thank you for the 1st on
the second one is that how does chloroethane undergoes nucleophillic substitution under fairly mild conditions and elimination under harsher conditions.
i can do how it goes under nucleophillic substitution and elimination but i cant find it in the given conditions.
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Elimination reaction: Something like alcoholic KOH or NaOH should do it.
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Substitution reaction: reaction with ammonia will form an amine.
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DoH! Did I just write 'warn NH3'! [:D]
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its OK
I got that you ment warM
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how can i evaluate the influence of structure and bonding on the course of reactions in "alkEnes undergo electrophillic addition whereas bezene undergoes electrophillic substitution?
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For alkenes, what kind of reactivity might we expect form the C=C bond? They have greater electron density than single bonds and they are accessible to external reagents because they are located above and below the plane of the double bond rather than between the nuclei, unlike like a sigma bond. Both electron richness and electron accessibility tells us that the C=C bonds should behave as nucleophiles, this is exactly why most common reactions of alkenes is their reaction with electrophiles. If we have ethene reacting with HCl, the reaction takes place in two steps, beginning with the alkene reacting with H+. Two electrons from ethene move to form a new sigma bond with...arg, my fingers are sore [:)]
Here: have a picture to see if that'll help
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http://upload.wikimedia.org/wikipedia/commons/5/5e/Electrophilic_reaction_of_bromine_with_ethene.png
With benzene, the aromatic rings are less reactive towards nucleophiles than alkenes are. So why does benzene not undergo addition? The simple answer is: If addition occured, the stability of the aromatic ring would be lost, energy would be absorbed, and the overall reaction would be unfavourable. When substitution occurs however, the stability of the aromatic ring is retained, energy is released and the reaction is favourable.
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how can i evaluate the influence of structure and bonding on the course of reactions in "alkAnes undergo free redical reactions?"
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how can i evaluate the influence of structure and bonding on the course of reactions in "the relative reactivities of halogenoalkAnes towards nucleophilic substitution?"
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how can i evaluate the influence of structure and bonding on the course of reactions in "the relative reactivities of carboxylic acids and acid chlorides towards esterification?"
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predict the products of the following industrail organic reactions and give the chemical equations involved
i) dehydration of ethanol using cold concentrated sulfuric acid
ii) oxidation of ethanol using acidified sodium dichromate solution at room temp
iii) coupling reaction of benzene diazonium chloride with phenyl amine
iv) refluxing of bezene with concentrated nitric acid and concentrated sulfuric acid
AND then give the reaction mechanisms for reactions given for the each of the above.
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Look LC
I know I am asking for too much but trust me we don't even know the names of few of the compounds
But still we are asked to do this.
I swear by my life we didn't do any of them in class neither the monster has given us any clue. You tell me what should I do.
In such conditions you are the only one I can ask to help for. [:(]
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how can i evaluate the influence of structure and bonding on the course of reactions in "alkAnes undergo free redical reactions?"
They have sigma bonds making the electrons less accessible to outside reactants. It (alkanes) is not particularly reactive so it requires a radical to break the C-H bonds.
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how can i evaluate the influence of structure and bonding on the course of reactions in "the relative reactivities of halogenoalkAnes towards nucleophilic substitution?"
The halogen atom(s) is more polar than the other atoms, so the nucleophile essentailly 'kicks' it out when it attacks, making the halogen an ion. Because the leaving group (the halogen) is expelled with a neagtive charge in most SN2 reactions, the best leaving groups are those that give the most stable anions, so most of the halogens are good leaving groups. All of these factors contributes to haloalkanes undergoing substitution.
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how can i evaluate the influence of structure and bonding on the course of reactions in "the relative reactivities of carboxylic acids and acid chlorides towards esterification?"
They both have the carbonyl group C=O, and esters do too. The carbon atom is attached to two highly electronegative atoms, as a result, there is a 'relatively' strong 'slightly positive' charge on the carbon. The non-bonding pair of electrons on the O-H group pf the alcohol attacks the slightly positive Carbon atom, resulting in substitution of the OH- or X- for the alcohol group, forming an ester.
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i) dehydration of ethanol using cold concentrated sulfuric acid
http://www.chemguide.co.uk/mechanisms/elim/dhethanol.html
ii) oxidation of ethanol using acidified sodium dichromate solution at room temp
http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html
iii) coupling reaction of benzene diazonium chloride with phenyl amine
http://www.chemguide.co.uk/organicprops/aniline/propsdiazo.html#top
Scroll down the page a bit, it's down there.
iv) refluxing of bezene with concentrated nitric acid and concentrated sulfuric acid
http://www.chemguide.co.uk/mechanisms/elsub/nitration.html
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They've got the mechanisms too.
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LC
do you have any links for the first three questions?
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No can do, I'm afriad.
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Hey LC
look at the question below;
explain the influence of molecular shape on the commercial uses of selected compounds
any four of the following;
alkanes
alkenes
halogenoalkanes
amines
alcohols
carbonyl compounds( aldehydes/ketones)
I couldnt find any link on the google so if you could please help or any link [:(]
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alkenes
www.albany.edu/faculty/musah/achm216a/presentations/chap7.ppt
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alkanes
I must say you get very weird questions.
http://en.wikipedia.org/wiki/Petroleum#Chemistry
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explain the influence of molecular shape on the commercial uses of selected compounds
amines
Very wierd.
http://en.wikipedia.org/wiki/Amine#Use_of_amines
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alcohols
Drink it [:)]
http://wiki.homedistiller.org/Alcohol_fuel
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Does your teacher ever give you an answer? Or like an exemplar on how you should go about answering these type of questions? If you do, post it so I know exactly what you are after otherwise I'm only clutching at straws here.
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My chemistry teacher has fallen sick for the past 1 week
So really don't know what he wants, all we have is the question sheet with us and we can only assume what he's looking for? [:-\]
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The question sheet is asking
"evaluate the need to separate isomers of organic compounds(the six compounds I mentioned in the last post) before they are used. in doing this you must consider how the isomers may be separated and the costs involved. this must be related to the need for a single isomer product or whether the presence of more than one isomer will significantly affect the performance of the product. examples of these may be found in the perfumery, flavourings and pharmaceutical industries."
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Yeah, and what have you written so far?
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all I've done so far is below; just confirm for me if I am on the right track. [:)]
Flavouring industry
Flavor in food is important in how food smells and tastes to the consumer, especially in sensory analysis. Some of these products occur naturally like salt and sugar, but flavor chemists (called a "flavorist") develop many of these flavors for food products. Such artificial flavors include methyl salicylate which creates the wintergreen odor anMolecules containing the same atoms but differently arranged, so that the chemical and biochemical properties differ. (1)In positional isomers the functional groups are on different carbon atoms; e.g. leucine and isoleucine.(2)D- and L-isomerism refers to the spatial arrangement of four different chemical groups on the same carbon atom (stereo-isomerism or optical isomerism). R- and S-isomerism is the same, but determined by a set of systematic chemical rules.(3)Cis- and trans-isomerism refers to the arrangement of groups adjacent to a carbon-carbon double bond; in the cis-isomer the groups are on the same side of the double bond, while in the trans-isomer they are on opposite sides.d lactic acid which gives milk a tart taste.
One of two or more substances with identical molecular formulas but different configurations, differing only in the arrangement of their component atoms. It usually refers to stereoisomers (rather than constitutional isomers or tautomers; Optical isomers, or enantiomers ( optical activity), occur in mirror-image pairs. Geometric isomers are often the result of rigidity in the molecular structure; in organic compounds, this is usually due to a double bond or a ring structure. In the case of a double bond between two carbon atoms, if each has two other groups bonded to it and all are rigidly in the same plane, the corresponding groups can be on the same side (cis) of the CC bond or across the CC bond (trans) from each other. An analogous distinction can be made for ring structures that are all in a plane, between isomers whose substituent groups are on the same side and isomers whose substituent groups are on both sides of the plane. Diastereomers that are not enantiomers also fall into this category. Most cis-trans isomers are organic compounds.
A physical separation method in which the components of a mixture are separated by differences in their distribution between two phases, one of which is stationary (stationary phase) while the other (mobile phase) moves through it in a definite direction. The substances must interact with the stationary phase to be retained and separated by it.
Retention results from a combination of reversible physical interactions that can be characterized as adsorption at a surface, absorption in an immobilized solvent layer, and electrostatic interactions between ions. When the stationary phase is a porous medium, accessibility to its regions may be restricted and a separation can result from size differences between the sample components. More than one interaction may contribute simultaneously to a separation mechanism. The general requirements are that all interactions must be reversible, and that the two phases can be separated (two immiscible liquids, a gas and a solid, and so forth) in such a way that a distribution of sample components between phases and mass transport by one phase can be established.
Perfumery industries
The term "perfume composition" is used herein to mean a mixture of organic compounds including, for example, alcohols, aldehydes (other than the aldehydes of our invention); ketones, nitriles (other than the nitriles of our invention), ethers, lactones, natural essential oils, synthetic essential oils, and frequently hydrocarbons which are admixed so that the combined odors of the individual components produce a pleasant and desired fragrance. Such perfume compositions usually contain (a) the main note or the "bouquet" or foundation stone of the composition; (b) modifiers which round off and accompany the main note; (c) fixatives which include odorous substances which lend a particular note to the perfume throughout all stages of evaporation and substances which retard evaporation; and (d) topnotes which are usually low-boiling, fresh smelling materials.
In perfume compositions, the individual component will contribute its particular olfactory characteristics, but the olfactory effect of the perfume composition will be the sum of the effects of each of the perfume ingredients. Thus, the 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures of our invention can be used to alter the aroma characteristics of a perfume composition, for example, by highlighting or moderating the olfactory reaction contributed by another ingredient in the composition.
The amount of the 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures of our invention which will be effective in perfume compositions, depends on many factors including the other ingredients, their amounts, and the effects which are desired. It has been found that perfume compositions containing as little as 0.5% of the 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures of our invention or even less can be used to impart sweet, lactonic, coumarinic, jasmine aromas with intense green, citrusy, sweet, lactonic topnotes and bergamot peel and lemony undertones to soaps, liquid and solid, anionic, cationic, nonionic and zwitterionic detergents, cosmetic powders, liquid and solid fabric softeners, optical brightener compositions, perfumed polymers and other products. The amount employed can range up to 50% or higher and will depend on consideration of cost, nature of the end product and the effect desired on the finished product and the particular fragrance sought.
The 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures of our invention can be used alone or taken together with other perfumery components in perfume compositions as an olfactory component in detergents and soaps, space odorants and deodorants; colognes, toilet waters, bath salts, hair preparations, such as lacquers, brilliantines, pomades and shampoos; cosmetic preparations such as creams, deodorants, hand lotions and sun screens; powders such as talcs, dusting powders, face powders and the like. When used as an olfactory component of a perfumed article, as little as 0.01% of one or more of the 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures of our invention will suffice to impart sweet, lactonic, coumarinic, jasmine aromas with intense green, citrusy, sweet, lactonic topnotes and bergamot peel and lemony undertones. Generally, no more than 0.5% is required.
In addition, the perfume composition clan contain a vehicle or carrier for the 3,5-dimethyl-pentenyl-dihydro-2(3H)-furanone isomer mixtures taken alone or taken together with other ingredients. The vehicle can be a liquid such as an alcohol such as ethanol, a glycol, such as propylene glycol or the like. The carrier can be an absorbent solid such as a gum (e.g., gum arabic, guar gum and xanthan gum), or components for encapsulating the composition such as gelatin which can be used to form a capsule wall surrounding the perfume oil as by means of coacervation.
Our invention also relates to the utilization of controlled release technology for the controlled release of perfumes into gaseous environments; odor maskants and deodorizing agents into gaseous environments from polymers such as mixtures of epsilon polycaprolactone polymers and polyethylene which polyepsilon caprolactone polymers are described at Column 65 of U.S. Pat. No. 4,956,481 the specification for which is incorporated by reference herein.
The terpenes form one of the most important groups of perfumery materials, including such products as geraniol, linalool, terpineol. camphor, cedrene, and their many derivatives. They occur widely in nature, and some are used as starting points for the synthesis of other materials, such as the ionones, and many of the modern woody chemicals. Before their structure and chemistry was fully understood, the terpenes were detined simply as the insoluble constituents of essential oils. It was found that the majority contained either 10 or 15 carbon atoms, the two groups being named mono- and sesquiterpefles. Other terpenes containing higher multiples of five carbon atoms were also known to exist in both plants and animals. The structure of these materials was subsequently explained by the working out of their biosynthesis.
All terpenes are in fact formed by the linking together of two or more units of five carbon atoms, originally thought to be molecules of isoprene, or isoprene units. This description is still used, although it is now known that the chains are based on the combination of two slightly different materials. isopentenyl pyrophosphate and dimethyl allyl pyrophosphate, which combine to form geranyl pyrophosphate. The addition of a further isopentenyl pyrophosphate molecule produces farnesyl pyrophosphate. These two materials, which are directly related to geraniol and farnesol. form the starting points from which all other mono and sesquiterpenes are derived:
Although, chemically, all products belonging to these two series are correctly described as terpenes, in perfumery (just to make matters even more complicated!) the word is often used in a narrower sense to describe only the hydrocarbon members of the series. These include limonene and terpinolene with 10 carbon atoms, and cedrene and caryophyllene with 15. Materials belonging to the series but containing oxygen are then described as terpenic alcohols, aldehydes, and so on.
Pharmaceutical industries
Thalidomide is racemic – it contains both left- and right-handed isomers in equal amounts. The (R) enantiomer is effective against morning sickness but the (S) is teratogenic and causes birth defects. The enantiomers can interconvert in vivo – that is, if a human is given pure (R)-thalidomide or (S)-thalidomide, both isomers can be found in the serum – therefore, administering only one enantiomer will not prevent the teratogenic effect.
hese two compounds are identical in every way and exist in equal proportions within the drug, except that they are nonsuperimposable mirror images of each other, he said. The two identical compounds are the result of rotation around the chiral carbon. Atoms can be oriented in either the right-handed or left-handed direction around the chiral carbon. The atoms of R isomers are oriented in the right-handed direction and those of S isomers are in the left-handed direction.
Although isomers are symmetric and mirror images of one another, they can have very different pharmacological properties, said Dr. Cerasoli. For instance, each isomer, in pure solution, bends polarized light in a certain direction. (R)-albuterol, also called levalbuterol, bends light in the left-handed direction. A natural example of isomer differences are the isomers of limonene: (S)-limonene is orange and (R)-limonene is lemon. These isomers interact differently with receptors on the tongue, enabling a person to perceive different tastes. Isomers can also have very drastically different behaviors, added Dr. Cerasoli. For instance, the S isomer of thalidomide is a potent teratogen whereas the R isomer is an anti-emetic and a sedative.
In 1992 the FDA restricted the marketing of racemates, drugs that are composed of equal proportions of two isomers. To market racemates, pharmaceutical companies must, in essence, develop and study three drugs: the racemate, the R isomer, and the S isomer. To avoid this, pharmaceutical companies now identify the active isomer and usually market isomerically pure products.
ß2-agonist isomers
Dr. Cerasoli summarized the beta-agonist controversy that occurred in the late 1980s. Following the release of two beta agonists, isoprenaline forte in 1966 and fenoterol in 1977, the mortality rate for asthmatics who were taking these drugs increased by three- and fourfold, respectively. One theory for the mortality increase is that these drugs are racemates and one of the isomers has deleterious pharmacologic properties.
Using current technology, the albuterol isomers were separated and it was determined that (R)-albuterol, or levalbuterol, is the beta agonist. (R)-albuterol binds to the beta2-receptor with high affinity whereas (S)-albuterol cannot bind. Biological receptors are stereospecific. (S)-albuterol has aberrant pharmacological activity that is actually very similar to asthma pathophysiology. (S)-albuterol increases eosinophil activation, histamine release, mucus production, intracellular calcium, and the release of several chemical mediators and cytokines. (S)-albuterol induces all the stuff that you don’t want to have going on in asthma, said Dr. Cerasoli.
A clinical study was undertaken to determine the efficacy and tolerability of levalbuterol (J Allergy Clin Immunol 1998;102(6 pt 1):943-52). By measuring FEV1 over a period of several hours, it was found that 1.25 mg of (R)-albuterol improves FEV1 to a greater extent and for a longer period of time than 2.5 mg of racemic albuterol even though the same amount of active bronchodilator was in each drug (1.25 mg (R)-albuterol). This suggests that (S)-albuterol within the racemic formulation is inhibiting the activity of (R)-albuterol, Dr. Cerasoli said. In fact, excellent bronchodilation can be attained with just 0.63 mg (R)-albuterol, and for children the dose can be dropped down to 0.31 mg.
If the (S)-albuterol is removed, the dose of (R)-albuterol required for effective bronchodilation can be lower, he said. An advantage of decreasing the dose of beta agonist is the corresponding decrease in side effects. For instance, tachycardia is reduced in patients who take levalbuterol versus those who take racemic albuterol. In this study, patients who took levalbuterol three times daily for four weeks had an improvement in their resting FEV1, whereas those taking racemic albuterol showed no improvement. Dr. Cerasoli also summarized a study of asthma patients who were admitted to the emergency department because of an exacerbation of asthma. In the U.S., standard nebulized treatment is 2.5 mg to 5.0 mg of racemic albuterol every 20 minutes three times followed by 2.5 mg to 10 mg every 1 to 4 hours as needed. In general, under this treatment plan, 67% of patients are discharged and 33% are admitted.
The mechanism of thalidomide's teratogenic action has led to over 2000 research papers and the proposal of fifteen or sixteen plausible mechanisms. A theoretical synthesis in 2000 suggested the following mechanism: Thalidomide intercalates (inserts itself) into DNA in G-C (guanine-cytosine) rich regions. Due to its glutarimide part, (S) thalidomide fits neatly into the major groove of DNA at purine sites. Such intercalation impacts upon the promoter regions of the genes controlling the development of limbs, ears, and eyes such as IGF-I and FGF-2. These normally activate the production of the cell surface attachment integrin αvβ3 with the resulting alphavbeta3 integrin dimer stimulating angiogenesis in developing limb buds. This then promotes the outgrowth of the bud (IGF-I and FGF-2 are also both known to stimulate angiogenesis). Therefore, by inhibiting the chain of events, thalidomide causes the truncation of limb development. In 2009 this theory received strong support, with research showing "conclusively that loss of newly formed blood vessels is the primary cause of thalidomide teratogenesis, and developing limbs are particularly susceptible because of their relatively immature, highly angiogenic vessel network.
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Does your teacher not object if you copy and paste your assignments off wikipedia? The first sentence I tried via google scored a direct hit...
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Basically I am not going to cut and paste it I just wanted to show it to LC if I am on the right track because if he approved it then I am going to USE these links not cut and paste because if I do that then it would be plagiarism and I will be disqualified from the course [:)]
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Well um... I still don't the kind of answers that you are expected to write. But sure, use that link, I'll be a brave man to argue against Wiki...