Heck Reaction

In the final blog assignment for Organic Chemistry we were to go to the website http://www.scs.illinois.edu/white/index.php?p=publications and pick a publication to read about and explain. From looking at the publications I chose "A General and Highly Selective Chelate-Controlled Intermollecular Oxidative Heck Reation". The Heck Reaction which is also referred to as the Mizoroki-Heck Reaction is a chemical reaction of unsaturated halides that contain a alkene, base, and a palladium catalyst to form a substituted alkene. The general reaction scheme is shown below:

                                                   http://en.wikipedia.org/wiki/Heck_reaction
This reaction shows how it is completed in the presence of a organopalladium catalyst. The halide which can consist of (Br,Cl) usually is a aryl, benzyl, or vinyl compound and the alkene contains at least one proton and is usually proton-deficient. The base consist of triethylamine, potassium carbonate, or sodium acetate. In addition, the catalyst contains palladium chloride or palladium acetate with the ligand containing triphenylphosphine or BINAP.
After reading over the article I concluded that they were examining the chelation effects by moving the oxidizing functionality away from the allylic position. Under the oxidized conditions, the acidic Heck reactions coupld rapidly synthesize 4-arylated-but-2-enoates and -enone just as single olefin isomers.
In conclusion, they showed a intermolecular Heck reaction coorelating to olefin in the cross-coupling method. The general catalyst Pd/bis-sulfoxide complex can catalyzes a chelate-controlled oxidative Heck reaction. In addition to this, electrophilic catalyst is senstitive to the chelation effect from oxygen and nitrogen which result in the regioselectivities for the olefin insertion.The reaction below shows the specific reaction mechanism for the Heck reaction.

                                                          http://en.wikipedia.org/wiki/Heck_reaction

I was not able to add the pictures from the publication however, you can read the article as well as seeing the results at http://www.scs.illinois.edu/white/pubs/pub11.pdf
   

Problem

In this week we assignment we were asked to come up with a problem from chapter 24 or chapter 26 as a test questioin. I will be discussing the Claisen Reaction from chapter 24. the Claisen reaction is known as the second general reaction of enolates with other carbonyl compounds. In this reaction two molecules of an ester react with each other in the presence of an alkoxie base to form a beta-keto ester. An example of a Claisen reaction is shown below:

In this reaction the products are known to be beta-ketoesters which can be useful for synthetic intermediates. The product in this equation is the original ester with a acyl group added on from ethyl ethanoate. A test question that could appear on the test would be draw the structure of the product that would be obtained from the following reagents. Problem number two represents the clasien condensation question. 

References:

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/crbacid3.htm

Extra Credit

Guest speaker Steven R. Myers presented the effects of tobacco smoking durnig pregnancy. There are many risk that come while smoking during pregnancy which include: miscarriages, stillborn babies, premature birth, low birth-weight babies, SIDS, and second hand smoke. During his presentation I found some interesting things out which included: during the first six to eight weeks of the pregnancy this is when the most harm can be done to the baby. In addition to this, the way they tested women smokers versus non-smokers during there pregnancy is using a biomarker which is defined as: anything that can be used in the body to follow it. With using biomarkers researchers are able to see the harms done to the baby while in the mother's womb.
One organic compound that was mentioned that is used in cigarettes was formaldehyde. Not only is this organic compound used in cigarettes but formaldehyde is also sold as a 37% aqueous solution known as formalin, which has been used as a disinfectant, antiseptic, and perservative for biological specimens. This compound is also known to be a combustion of coal and other fossil fuels which is partly responsible for the irration caused by smoggy air. The following picture below shows formaldehyde:

Hell-Volhard-Zelinsky halogenation

The Hell-Volhard-Zelinsky halogenation mechanism halogeantes carboxylic acids at the alpha carbon. In this reaction it takes place in the absence of a halogen carrier. From here the reaction can be initiatied by the addition of a catalytic amount of either PCl3, PBr3, red phosphorous, or Br2. The standard mechanism of this is shown below:

 
This mechanism shows how PBr3 replaces the carboxylic OH with a bromide which results in the carboxylic acid bromide. At this point the acyl bromide can be tautomerize to an enol, which will react with the Br2 a second time at the alpha poisition. In addition to this, the reaction depends on the enol type character of carbonyl compounds as well as the product of the reaction, an alpha-bromocarboxylic acid can be converted by substitution reactions to either a alpha-hydroxy or a alpha-amino carboxylic acid.
An example that I found where the Hell-Volhard-Zelinsky halogenation process occured is shown below:

This reaction shows that using PBr3 with Br2 also known as an intermediate acid bromide is formed which undergoes enolization and bromination. 

Refernces:
1.Hell-Volhard-Zelinsky halogenation. Wikipedia the encyclopedia. 21 April 2011. http://en.wikipedia.org/wiki/Hell-Volhard-Zelinsky_halogenation.

2. Jie Jack Li. Hell-Volhard -Zelinsky halogenation. http://www.springerlink.com/content/t2ur113r36720270/.

Benzyl Butyrate

Benzyl Butyrate contains a molecular formula of C11H14O2, a boiling point of 240 °C, density of 1.009 g/mL, contains a boiling point between 238.00 to 240.00°C. A picture of benzyl butyrate is shown below: 

Benzyl Butyrate is known to be a clear colorless liquid in appearance and contains a strong fruity odor like apricots. However, other researchers say that it smells like flowers. Benzyl butyrate is derived from benzyl alcohol and butanoic acid. The reaction for this is shown below:

CH3CH2CH2-COOH + C6H5CH2OH ---------------->    C11H14O2
            


Benzyl Butyrate is soluble in alcohol and is used in perfume companion as a modifier for to benzyl acetate and benzyl propionate. In addition to this, the compound is used in flavoring as well as plactizier (something that makes plastic less rigid by breaking up the molecules). An example of this ester reacting to form a carboxylic acid derivative would be benzyl butyrate and benzyl alcohol can be converted to a carboxylic acid derivative by merely undergoing the reaction with a aldehyde which would give the carboxylic acid since aldehyde's convert benzene rings to carboxylic acids.  

Organolithium Reaction

An organolithium is known as an organometallic compound that contains a direct bond between a carbon and a lithium atom. An example of a organolithium is shown below:


In this diagram it shows how the reagents are typically prepared by reaction of an alkyl halide with the corresponding metal. Since this mechanism uses lithium (Li), the halogen and the metal exchange to form the organolithium reagent. In addition to this, the IUPAC name of the product would be: 2-cyclopentylacetophenone. In part B this shows the organolithium being used in the reaction when the starting product is reacted with t-BuLi. With that in mind, the new c-c bonds are formed in the product that is labeled with the 2 under it. These new c-c bonds are the benzene ring that is formed as well as the ketone bond formed.

Amino Acid

Glutamic acid is one of the twenty proteinogenic amino acids. It can be abbreviated either Glu or E. This amino acid is a non-essential amino acid. Glutamic acid is a key molecule in cellular metabolism, and is abundant in both animal and plant protein. However, in humans it is a non-essential amino acid because the body is able to produce it's own glutamic acid. In addition to this, the dietary proteins are broken down by digestion into amino acids which play as a metabolic fuel for other functional roles in the body.  A picture of glutamic acid is shown below:

The pKa value of carboxyl group for glutamic acid in a polypeptide is about 4.3. This may be a little high for a pKa value due to the inductive effect of the additional methylene group. The isoelectric point is around 5.65. Pka values are shown below in the diagram:

 

Glutamic acid can be easily converted to proline; due to the carboxyl group is reduced to the aldehyde. From here the aldehyde can react with the alpha-amino group which eliminates water. A diagram of this is shown below:

Electrophilic Substitution

This weeks goal was to find a peer review journal which shows a picture of an electrophilic substitution and why it is important in Organic Chemistry. After doing research on electrophilic substitution it can be defined as: a form of substitution reaction in which the leaving group (normally hydrogen) is replaced with an electrophile. It is important because it a way of introducing functional groups onto a benzene ring. There are two types of substitution one known as electrophilic aromatic substitution and electrophilic aliphatic substitution. Common aromatic substitution include: aromatic nitration, aromatic halogenation, aromatic sulfonation, and Friedel-Crafts, and common ones for aliphatic substitution include: nitrosation, ketone halogenation, and ketol-enol tautomerism,   A picture is shown below which shows electrophilic substitution:

This digram shows electrophilic aromatic substitution in which the final step is a decarboxylation rather than a deprotonation. This is due to the ketone carbonyl. 

References:

1. UC Davis ChemWiki. Section 15.5 Electrophilic aromatic substitution. 4 Feb. 2011. 6 March 2011.

<http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter_15:_pi_electrons_as_nucleophiles/Section_15.5:_Electrophilic_aromatic_substitution>. 

Aromaticity

 Hi Grandma,

In class we have been talking about benzene rings, the functions of these compounds, as well as aromaticity. However, for you to even understand what this means I need to explain some of the terms. For compounds to be aromatic they must meet four conditions which include: it must be a ring, it must be flat(planar), it must have in each atom of the ring a p orbital that’s orthogonal to the plane of the ring. In other words, the atoms in ring are sp² hybridized, and it must have a Huckel number of pi electrons, which must follow the 4n+2 rule.

                With knowing these rules let’s look further in dept of ways to classify all other compounds which include: if the molecule meets the first three conditions, but only contains 4nπ electrons the molecule is considered to be anti-aromatic. However, if the molecule fails any or the first three conditions then the molecule is considered to be non-aromatic. Now with a little bit of background let’s now explore the conditions a little bit more in depth. Condition one it must be a ring means that only rings can be aromatic; acyclic (having an open chain structure) systems cannot be aromatic. The second condition it must be flat deals with the shape of the ring. Ring systems can be planar (flat) or three-dimensional. Most conjugated ring systems tend to be flat so that it maximizes the overlap between the p orbital’s. An example would be naphthalene which is planar, and cyclodecapentaene is nonplanar due to two of the hydrogen’s. Both examples are shown below.

                 

           (naphthalene)                                                                                                        (cyclodecapentaene)

           (planar showing aromactity)                                                                          (nonplanar due to two H’s).

The third condition deals with the p orbital’s. An aromatic system must have an unbroken ring of p orbitals, so that any ring that contains a sp³ hybridized carbon will not be aromatic. For example cycloheptatriene is non-aromatic due to the fact that one of the ring carbons is sp³ hybridized. However, carbocations’ (which have a positively charged carbon) are sp² hybridized (and contain an empty p orbital); with this cycloheptatriene cation has an unbroken ring of p orbitals and is an aromatic compound. An example of this is shown below.

                                          

The fourth condition deals with Huckels rule. A tricky aspect that comes into play with Huckels rule is that you must remember of counting the number of pi electrons in the pi system when the ring contains heteroatoms like O, S, N. So how do you know which lone pairs to count as part of the pi system and which to ignore. The general rule of counting substituent’s to determine the hybridization holds true, it does fail when the atom contains a lone pair which is adjacent to a double bond; which means when it is conjugated. A diagram of pi electrons is shown below:

Pi electron Counts

Integer(n)	Aromatic Numbers (4n+2)	Anti-aromatic numbers (4n)
0	2	--
1	6	4
2	10	8
3	14	12
4	18	16

After reading this letter grandma I hope that it gives you a little insight on what aromaticity means and how it relates to benzene rings. 

Muddiest Point

When looking over Chapter 13 one of the muddiest points for me is looking at infrared spectroscopy data and determining what the compound may be. Infrared spectroscopy can be defined as measuring the absorption of the infrared radiation of organic compounds. However, for the absorption to occur the energy of the photon must match the difference of the energy between two states. When a molecule absorbs radiation from the IR it can cause the bonds to bend, stretch which can cause deforming bond lengths and angles. So since different kinds of bonds vibrate at different frequencies they can absorb different frequencies of IR radiation, which then the functional group can be determined. To determine a particular bond on the IR spectroscopy one must look at   the bond strength and atom mass due to the fact that bonds form into four predictable regions of an IR spectrum.

References:

1. Characterization techniques for Organic Compounds. 25 January 2011. <http://www.chem.uky.edu/courses/che232/FTL/C1309.pdf>.

2.Infrared Spectroscopy. 25 January 2011. <http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm>.

3. Infrared Spectroscopy. 25 January 2011. <http://www.prenhall.com/settle/chapters/ch15.pdf>.