The final blog assignment for this semester is to visit the web page of Christina White of University of Illinois Urbana: Champaign and find an article of interest and relate it to topics discussed in recent chapters. A publication that I found that interest me was titled "A General and Highly Selective Chelate-Controlled Intermolecular Oxidative Heck Reaction". The general reaction scheme is illustrated below.

In this cross coupling heck reaction, palladium/sulfide is used as a catalyzed to react
organoboron and olefins which resulted in a wide range of selectivites. This publication described the observed benefits of using a Heck reaction for complex molecular synthesis.

The general description of the reaction, as described in the in text publication found on the website, was fairly difficult to understand. Though many aspects were familiar, such as the use of palladium as a catalyst and the description of the general Heck reaction. I enjoyed reading this article, it brought what I have learned in organic 2 and took it a few steps further. 

Resources:
http://www.scs.illinois.edu/white/pubs/pub11.pdf

Sample Test Question

Draw the starting materials needed (in the presence of LDA) to prepare this compound.

Step 1. Identify the alpha and beta carbons adjacent to the carbonyl group.

Step 2. Break the C-C bond between the two carbons

Answer: A carbonyl compound and an enolate is required to make this compound

Seminar Critique

The topic of this chemistry seminar was the affects of tobacco smoke on unborn children. Led by Dr. Steven Myers, the effects of tobacco, and the various adverse affects it has on the the development and well being of a unborn fetus as well as a newborn child were described. Dr. Myers is a faculty of University of Louisville Medical School and specializes in the Pharmacology/Toxicology department.

Prior to attending this seminar, I was much aware of the negative affects cigarette smoke had on a pregnancy, but after attending, the depth of my knowledge greatly increased. The various chemical found in cigarette smoke were discussed during the seminar. Dr. Myers described how the increased concentrations of these chemicals in the vicinity of a developing fetus can increase the likelihood of defects in the child. These abnormalities include, but are not limited to, cardiorespitory defects, neurological problems and SIDS (sudden infant death syndrome). One such chemical, 4-aminobiphenol, is particularly hazardous. As stated by Dr. Myers, it one of the most carcinogenic compounds known.

Molecular Weight: 169.22
Melting Point: 55 deg.C
Boiling Point: 302 deg.C

Hell-Volhard-Zelinsky Halogenation

The Hell-Volhard-Zilinsky Halogenation is a reaction in which the alpha carbon of a carboxylic acid is halogenated. This reaction is catalyzed by a necessary amount of PBr2, which replaces the OH, thus forming an acid bromide. The acyl bromide then tauteramerizes to form an enol. A molar amount of Br2 is also added, which bonds to the alpha carbon. This reaction differs from other halogenations in that it does not include a halogen carrier. The general reaction scheme of a Hell-Volhard-Zelinsky Halogenation is illustrated below.



A reaction involving the Hell-Volhard-Zelinsky Halogenation is the synthesis of 2-bromobutanoic acid, also called 2-bromobutyric acid, from butanoic acid.

Formula: C4H7BrO2

Molecular Weight: 167 g/mol

Melting point: -4 deg C

Boiling point 101 deg C

A reaction scheme of this reaction is illustrated below.

References:

http://en.wikipedia.org/wiki/Hell-Volhard-Zelinsky_halogenation

http://www.colvir.net/prof/carl.brabant/Faidherbe/acides.htm

Propyl Acetate

Propyl Acetate is a common solvent used as a flavoring due to its fruity taste. It is colorless and emits the odor similar to pears. Propyl acetate has a 2% water solubility and is miscible in most organic compounds. The structure and mass spectrum for Propyl Acetate is represented below.

Molecular Formula: C5H10O2 

Boiling Point: 216 deg. F (102 deg. C)
Freezing temperature of -139 deg F ( -95 deg C).
Density: .888 g/cm^3
Molecular Weight: 102.131 g/mol

Propyl acetate is formed by the esterifcation of acetic acid and 1- propanol by means of Fischer/Speier esterification.

My search for a reaction dealing with the conversion of propyl acetate into a carboxylic acid yielded no results, I did find some reaction involving propyl acetate used in distillation, though no carboxylic acids were formed. I searched the organic synthesis website supplied by Dr. Mullins and still had no luck, if any such reaction could be found by anyone, it would be much appreciated.

Thank for reading!!

Sources:

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

http://msds.chem.ox.ac.uk/PR/propyl_acetate.html



Grignard Reaction

Our assignment this week was to locate a reaction containing either a organolithium, organocuperate or grignard reagent. I chose one containing the Grignard reagemt. A Grignard reagent is an alkyl or aryl magnesium halide that acts as a nucleophil and attatcks a electrophilic carbon that are polar bonded to another carbon atom.The reacton I chose was the synthesis of N,NDIBENZYL-N-(2-ETHENYLCYCLOPROPYL)AMINE.

This reaction involves the reaction of N,N - dibenzylformamide (in red) with the grignard reagent,  3-butenylmagnesium bromide (in green). The Grignard reagent is added dropwise for 30 minutes resulting in a temporary black precipitate which requires a stirring for an additional hour.

The resulting product,  N,N-Dibenzyl-N-(2-Ethenylcyclopropyl)Amine, results in the formation of two new C-C bonds (shown in yellow) forms a three carbon ring. The resulting product is a yellow silicon gel.



Tryptophan

Tryptophan is an essential amino acid used by the human body. It is abreviated W or Trp and has an IUPAC name of (2S)-2-amino-3-(1H-indol-3-yl)propanoic acid. There are two sterioisomers of tryptophan, the L and D sterioisomers, but only the L is found in the human body system, the D is only found in naturally produced peptides. Its structure is represented below.

Tryptophan has a amine group, a caboxylic acid and a indole functional group. The pKa values for each functional group are as follows:

carboxyl - 2.39

Amino - 9.39

indole - 16.2

isoelectric point - pH- 5.89

The indole ring, located on the beta carbon, is the most significant, have the capability to hyrdrogen bond donate and thus the nitrogen is often in contact with solution. Tryptophan is used as a precurser for the neurotransmiter serotonin and the vitamin niacin. The group of peptides known as cystine peptides contain tryptophan.

Electrophilic Aromatic Substitution Journal

This weeks blog assignment was to locate a peer reviewed journal article containing an electrophilic aromatic substitution reaction. It was difficult to find an article outside of the CU database, but I was able to have some luck. The article that I chose contained not just one, but many simple EAS reactions. The article, Average Local Ionization Energies on the Molecular Surface of Aromatic Systems As Guides to Chemical Reactivity, published by Per Sjoberg, compares the reactivites of various electrophiles on benzene, to form many derivatives.The results were compared in a table showing the relationship between each compound and the various energies released during the formation of each compound.The relative reactivity with an electrophile is determined in this experiment by the strenght of the l(r) value. The lower ethe l(r) value, the more reactive the substance will be with the electrophile.

 The article analyzes benzene derivatives such as toluene, aneline, benzoic acid, and 1-florobenzene and determines the relative reactivity of the electrophile in each compound (CH3, NH2, F. COH...) The tendencies of each electrophile are analyzed and recorded. I found this article particularly interesting, it was simple to understand at an undergraduate level, yet still was able to provide new, valuable information. Posted is a link to the article.

http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=68&issue=8&startPage=1440

Source:

SjobergLast, Per. "Average Local Ionization energies on the molecular surface of aromatic systems as guides to chemical reactivity." Can J. Chem. 68. (1990): 1440-44. Print

Aromaticity

All organic compounds are classified as either aliphatic or aromatic. Aliphatic molecules are those that contain carbon chains with single and possibly double bonds. Aromatic compounds demonstrate properties that make them particularly special. Because of their structure, aromatics are stable and only undergo specific reactions. Benzene, shown below, is the most common aromatic compound.

There is a specific set of criteria by which a molecule must meet to be considered aromatic.

·         They are found in a ring structure that is in a circular pattern with alternating double bonds. This property identifies them as cyclic molecules.

·         They are planar, which means they can be drawn in a single plan dimension.

·         Aromatic compounds also have conjugated double bonds, meaning the electrons surrounding the double bonds overlap those found on nearby adjacent atoms.

·         They must also obey Hϋckles Rule, which states that that all the bonding orbitals must be full. An equation used to determine this is 4n+2, with n being a positive integer. Benzene for example has 3 π bonds, and therefore 6 π electrons ,(2 electrons per bond), the equation is written as

4n+2 = 6

n =1

Since n = 1 = positive, the rule is satisfied and thus the compound, in this case benzene, is indeed aromatic.

Absent from the exam???

. 
There was much material not present on exam 1 that I expected to be. One question i found to be absent from the exam was the chemical shift calculation (parts per million). Discussed on pages 495-496 of chapter 14, the chemical shift is calculated by dividing the observed chemical shift (Hz) down field from the TMS, by the frequency of the NMR spectrometer. Also absent from the exam was the calculation for frequency and the ratios between different NMR chemical shifts. To find the frequency of the NMR spectrometer, you simply multiply the observed chemical shift (Hz) and the chemical shift (ppm) and you will get the frequency of the NMR spectrometer in MHz.

Also absent from the exam was the problems involving drawing charged mass spectrum fragments given the m/z values. This is done by calculating the appropriate number of carbon and hydrogen atoms compared to the given m/z value and arranging them likewise.

Muddiest Point

Follow the first week of semester, my most unclear point would have to be the the patterns in Mass Spec. plots. This concept was covered on the in class powerpoint. I have trouble determing the possible identities of the compounds simply by looking at the plots. I know there are characteristic patterns associated with each functional group but have to grasp the concept. I know, though that with more practice and studying, I can see a clear correlation in the plots and find a pattern associated with the functional groups.