Types Of Substitution Reactions Biology Essay

Types Of Substitution Reactions Biology Essay In a substitution reaction, a functional group in a particular chemical compound is replaced by another group .In organic chemistry, the electrophilic and nucleophilic substitution reactions are of main importance. Organic substitution reactions are classified into depending on whether the reagent that brings about the substitution is considered an electrophile or a nucleophile, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical or whether the substrate is aliphatic or aromatic. A reaction can be made faster or slower by taking into consideration the temperature and the solvent we are using.A good example of a substitution reaction is the photochemical chlorination of methane forming methyl chloride. Nucleophilic substitution What is a nucleophile Nucleophilic substitution happens when the reagent is a nucleophile, which means the attacking species is a nucleus loving species .it is itself negatively charged or has a lone pair. Such species get attracted to positive or electron deficient carbon centres.. A nucleophile reacts with an aliphatic substrate in a nucleophilic aliphatic substitution reaction. These substitutions can be of two dofferent mechanisms: unimolecular nucleophilic substitution (SN1) and bimolecular nucleophilic substitution (SN2). The SN1 mechanism has two steps. In the first step, the leaving group leaves, forming a carbocation. In the second step, the nucleophilic species attacks the carbocation and forms a sigma bond. This mechanism can result in either inversion or retention of configuration. An SN2 reaction has just one step. The attack of the reagent and the expulsion of the leaving group occurs simultaneously. This mechanism always results in inversion of configuration. When the substrate is an aromatic compound the reaction type is nucleophilic aromatic substitution. Electrophilic substitutions What is an electrophile An electrophile is a electron loving species, it itself is positively charged and wants to stabilize itself by making a sigma bond with the electron rich carbon centre. Electrophiles are involved in electrophilic substitution reactions and particularly in electrophilic aromatic substitutions. SN1 REACTION The SN1 reaction is a substitution reaction. SN means nucleophilic substitution and the 1 represents the fact that the rate-determining step is unimolecular . Carbocation intermediate is formed in this reaction .It is seen that tertiary carbocations are very stable due to + I effect and thus go for SN1 Reaction. With primary alkyl halides, the alternative SN2 reaction occurs. As primary Alkyl Halides mostly Form primary carbocation which is very unstable and thus have to go through SN2 Substitution reaction. Mechanism An example of a reaction taking place with an SN1 reaction mechanism is the hydrolysis of tert-butyl bromide with water forming tert-butyl alcohol: This SN1 reaction takes place in three steps: Formation of a tert-butyl carbocation by separation of a leaving group (a bromide anion) from the carbon atom: this step is slow and reversible. Nucleophilic attack: the carbocation reacts with the nucleophile. If the nucleophile is a neutral molecule (i.e. a solvent) a third step is required to complete the reaction. When the solvent is water, the intermediate is an oxonium ion. This reaction step is fast. Deprotonation: Removal of a proton on the protonated nucleophile by water acting as a base forming the alcohol and a hydronium ion. This reaction step is fast. WHY THIS REACTION OCCURS Bulky atoms(methyl, ethyl) surrounding the carbon atoms mostly allow SNI reaction. As the bulky alkyl halides are attached to the central carbon atom,it is both stabilized by hyperconjugation and +In ductive effect. The SN1 mechanism therefore dominates in reactions at tertiary alkyl centers and is further observed at secondary alkyl centers in the presence of weak nucleophiles. SN2 REACTION The SN2 reaction (also known as bimolecular nucleophilic substitution or as backside attack) is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophilic center and bonds to it, expelling another group called a leaving group. Thus the incoming group replaces the leaving group in one step. Since two reacting species are involved in the slow, rate-determining step of the reaction, this leads to the name bimolecular nucleophilic substitution, or SN2. Among inorganic chemists, the SN2 reaction is often known as the interchange mechanism. REACTION MECHANISM The reaction most often occurs at an aliphatic sp3 carbon center with an electronegative, stable leaving group attached to it X frequently a halide atom. The breaking of the C-X bond and the formation of the new C-Nu bond occur simultaneously to form a transition state in which the carbon under nucleophilic attack is pentacoordinate, and approximately sp2 hybridised. The nucleophile attacks the carbon at 180 to the leaving group, since this provides the best overlap between the nucleophiles lone pair and the C-X s* antibonding orbital. The leaving group is then pushed off the opposite side and the product is formed. If the substrate under nucleophilic attack is chiral, this can lead, although not necessarily, to an inversion of stereochemistry, called the Walden inversion. SN2 reaction of bromoethane with hydroxide ion. The products are ethanol and a bromide ion. In an example of the SN2 reaction, the attack of OH- (the nucleophile) on a bromoethane (the electrophile) results in ethanol, with bromide ejected as the leaving group. SN2 attack occurs if the backside route of attack is not sterically hindered by substituents on the substrate. Therefore this mechanism usually occurs at an unhindered primary carbon centre. If there is steric crowding on the substrate near the leaving group, such as at a tertiary carbon centre, the substitution will involve an SN1 rather than an SN2 mechanism, (an SN1 would also be more likely in this case because a sufficiently stable carbocation intermediary could be formed.) In coordination chemistry, associative substitution proceeds via a similar mechanism as SN2. FACTORS AFFECTING REACTION 1) The Basicity of the Leaving Group. By comparing the relative SN2 reaction rates of compounds with atoms in the same periodic group (the halides, for example), results show that the ability as a leaving group during an SN2 reaction depends on its basicity. In general, the weaker the basicity of a group, the greater its leaving ability. For example, the iodide ion is a very weak base and because it is so, it is the most reactive. Weak bases do not hold their electrons tightly, making it easier for their bonds to be broken. In contrast, the fluoride ion is a stronger base than the other halides and, therefore, the least reactive. In fact, the fluoride ion is such a strong base that compounds involving them essentially do not undergo SN2 reaction. Looking at the periodic table, relative basicity decreases down a group. (Stronger Base) F- > Cl- > Br- > I- (Weaker Base) 2) The Size of the Nucleophile. How readily a compound attacks an electron-deficient atom also affects an SN2 reaction. As a rule, a negatively charged species (e.g. OH -) are better nucleophiles than neutral species (e.g. H2O, water). There is a direct relationship between basicity and nucleophilicity: stronger bases are better nucleophiles. Acidity, the ability of an atom to give up a proton (H+), is comparatively relative in molecules whose attacking atoms are approximately the same in size, the weakest going toward the left side of the periodic table. If hydrogen were attached to second-row elements of the periodic table, the resulting compounds would have the following relative acidities: (Weaker Acid) NH3 If each of these acids were to give up a hydrogen, the result would be its conjugate base, and the relative strengths will reverse. The stronger base now moves toward the left side of the periodic table. (Stronger Base) -NH2 > HO- > F- (Weaker Base) Elements increase in size down the periodic table. Although basicity decreases down the periodic table, nucleophilicity increases as size increases depending on the solvent used. 3) Solvent. If a reaction is carried out in a protic solvent, whose molecules have a hydrogen bonded to an oxygen or to a nitrogen, the larger atom is a better nucleophile in an SN2 reaction. In other words, the weaker base is the better nucleophile in a protic solvent. For example, the iodide ion is better than a fluoride ion as a nucleophile. However, if the reaction is carried out in an aprotic solvent, whose molecules do not have hydrogen bonded to an oxygen or to a nitrogen, then the stronger base is the better nucleophile. In this case, the fluoride ion is better than the iodide ion as a nucleophile. 4) Sterics. Steric hindrance is any effect of a compound due to the size and/or arrangement of its substituent groups. Steric effects affect nucleophilicity but does not affect base strength. A bulky nucleophile, such as a tert-butoxide ion with its specific arrangement of methyl groups, is a poorer nucleophile than an ethoxide ion with a straighter chain of carbons, even though tert-butoxide is a stronger base.

The Witches Of Salem :: essays research papers

When I started reading, my impression was that this whole witchcraft test would be rather childish, and aimed toward elementary students. As I took the test the first time, I was feeling as if parts of it were somewhat pointless. Then as the test progressed on it started to get better. However, when I chose not to confess to something I didn’t do, I felt as if the was a little bit of a problem with the reasoning of these people. They didn’t let me get a word in edgewise, and on top of that, the judges seemed to favor the girls and only their opinions. It was almost as if the court wanted to condemn a lot of people to death or Hell, and they were allowing a young girl to be the ringleader.   Ã‚  Ã‚  Ã‚  Ã‚  But then again, when I was taking the test, a few thoughts crossed my mind about the whole trial and some of the thoughts of the people involved. One thing that puzzled me was why anyone would not be intelligent enough to say something while on the stand like, â€Å"I am not a witch, and I love God. And I am with the Lord.† And then start reciting the Ten Commandments. Something like that would blow the court away, and the judges wouldn’t know what to say to that, because it is totally the truth. But then another thing crossed my mind, maybe because of the times, and the little education of the people involved. In any case either the women did not wish to speak out, or they were unable to think so quickly on their feet of such comments. This is unfortunate because maybe if they were able to be so witty with the truth, then some lives might have been spared. However, it might not have worked at all, because when people are under pressure it is harder for them to think clearly. All in all I felt the experience was good and helpful too. It gives a better understanding of what it was like to live in Salem during the unjust accusatory trials. The experience of the test was extremely real, and did make me feel a little uneasy, due to all the questioning and harsh accusations.

Public Relations in college Athletics Essay

Public relations play important role in linking college athletics with other colleges and news media. It represents college athletics related issues to media level. Public relation is responsible for handling all communication and information exchange between the college and athletics and media. It also promotes and develop relations with other colleges and universities.   Public relations will also keep news site updated to keep inform the community about the current issues, updates and goals.   Public relation program will handled all media related inquires, it regularly updates about recent research carried out in the faculty, promote inter-colleges sports and workshops, other promotional programs in the community and many other activities on the campuses.   Public relation facilitates inter-departmental, inter-community and social relations.   Assessment:   College athletic public relations goal is to develop such programs to maintain good public relations with the community and to promote student athletics sports, moral, physical, social and emotional growth. Such programs will keep individuals involve with creative activities and simultaneously promote their social relations with the community, a sense of responsibility and increase their morals.   Plan or board policy in relation to an existing public relations/marking plan or program One of the main purposes of the public relations is to let the students and community learn college rules and regulations and respect it in all circumstances in order to provide well-balanced education and creative skills.   Public relations board will responsible for making new guidelines and policies for people especially parents and guardians to keep them update of regulations and procedures.   Public relations board will develop such policies in order to keep details of all programs and guidelines for the community, guardians and students. The policies must define and update the student’s and communities needs. It must also prepare information regarding programs to give student and guardians full information. Evaluation: According to a recent research (Parry and Hayden, 1993) postgraduate students benefit from the program only when these students are paid attention separately, faculty and departmental staff clearly verify the assistance these students should receive. For recruiting more students in postgraduate program following strategies are needed to be implemented in the new curricula. These strategies are formed after careful analysis of the problems that were faced by the students, which were causing decline in students’ strength in the university. Creative ideas were generated to find out various possible number of solutions for the prevailing problems.   Recruitment and selection of students   There is a need to develop a unique workable policy for accommodating minimum or maximum number of students in the postgraduate program on the basis of preferred recruitment practices and on the university standards to recruit students per class.   There is also a need to start scholarships for students who are unable to pay their full fee.   Technical expertise and competencies in their language should be considered mandatory prior to admission.   Apart from quantitative analysis of students’ recruitment, university should also consider the qualitative approach to recruit students. Thus, admitting those students who are skillful and eligible for the program. And who will prove to be good in giving out results, thus, improving the standards of university in terms of qualitative education.   Audit of an existing safety or crisis prevention plan Staff and supervisors All staff and supervisors should be highly qualified and experienced. Per supervisor and staff, students allocated should be evaluated. Number of supervisor allocated per faculty should be evaluated New developmental strategies for students, supervisors and staff For every student there should be a clear statement for the academic mission of the university and department, research achievements, focus of teaching at the university, discipline rules that are to be followed. Every student should have a clear idea about departmental activities, social and intellectual prospects, facilities, resources, services, support, research facilities, and other procedures. In addition, there should be accommodation facilities, offices for mail typing, laboratory space, technical support, research equipment, computerized infrastructure, photocopying, library facilities, telephone, email and facsimile facilities, research grants and paid work. All above mentioned facilities should be publicized among undergraduate students, who might get interested in taking admission in postgraduate. Recent research showed that postgraduate students find various elements useful such as outline of the research they are taking, opportunity to meet other postgraduates, academics, administrative, technical staff and faculty. Selection of topics should be made easy and should be in consistent with the research facilities and financial resources available in the department. Each student should be guided individually that how they have to conduct research. Each student should be encouraged to acquire specialist assistance in writing thesis, computing, analysis of data, researching in library and archives in the management database. Using recommended assessment techniques,    There should be regular meetings and discussions between the supervisors, other research students for keep check on the progress of work and new innovative ideas that research students might learn from each other. Each student should keep a record of his or her work. Similarly, each supervisor should keep record of their supervision to avoid any misunderstanding between student and the supervisor. There should be brief records of meetings, discussions, deadlines set for the accomplishment of certain task or research work, notes on advice provided to each student, photocopies of other important notes, drafts and student diaries. Working relationship with other students should be kept in harmony. Students should have opportunities to mix socially with other departmental students. There should be network of students to get mixed with each other and learn each other problems, research and learning abilities. Progress of each student should be completely checked. There should be a definite policy to monitor the continuous progress of students. There should be new developmental policies to provide financial assistance for research and other postgraduate students. Each student should keep participating in conferences, seminars and colloquia for sharing their knowledge with other research scholars of the same fields. Create an assessment tool to evaluate a program,    The program’s success depends on individual outcomes, hence, it is important to judge whether these outcomes are worthwhile or just achieved. The desired outcomes of this program are listed below. It will improve motor skills of a student and he would improve his locomotive and perceptual motor skills The program will enhance their learning and memorizing capability. A student will be able to give more attention to his studies. The student will develop better social relations. He would be better off in school and at home. Student’s emotional and psychological development will improve. Emotional problems are usually correlated with his physical, social and cognitive development. But as his cognitive, social and physical development enhances, his emotional development will improve. The program will improve quality of education at school. The student after being trained will have better skills to interact with his environment and will yield better results. The program is cost effective and will safe cost of future problems that may arise due to lack of education and training at this age. The program will speed up student’s cognitive development. The program is not offered for a specific need but it will improve overall development and generalized needs of a student. Teachers and trainers will find it easier to train through this program rather than typical way of teaching. â€Å"Building and modeling caring relationships is crucial to the preservice teacher’s capacity to receive curricular content and their ability to teach that content to young student.† (Lake, Jones, & Dagli, 2004) The program would be able to preserve social and morel values through better education and training of a student. As student are major and most crucial beings in transmitting such values. The program protects student’s right to live and develop to their full potential while benefiting from the environment. References    Lake, Jones, & Dagli (2004) Handle With Care: Integrating Caring Content in Mathematics and Science Methods Classes. Journal of Research in Childhood Education Vol. 19, Nos. 1 & 2, Fall 2004 and Winter 2004 Parry, S. and M. Hayden. 1993. â€Å"Supervising Higher Degree Research Students.† Canberra: Australian Government Publishing Service.   

Free Essays on Criminal

Deep within the word, â€Å"American† is its association with Race. To identify someone as Hispanic is to say very little, we need the adjective â€Å"white† or â€Å"Latino† or â€Å"colored† to make our meaning clear. In this country it’s the reverse. American means white and that’s it, and Latinos struggle to make the term applicable to themselves hyphen after hyphen and so on. Because American means white, those who are not white are presumed to be recent arrivals and often told to â€Å"go back to where they came from.† Thus we appear to operate within the dichotomized racial categories of American/non-American; these are racial categories, because they effectively mean white/nonwhite (17). This is the reason why I believe race in the United States has indeed been socially constructed is through stereotypes and lack of knowledge. The comparison between â€Å"whites† and â€Å"Latinos† are very different and how each of the group is perceived is very different. A "stereotype" is a generalization about a person or group of persons. We develop stereotypes when we are unable or unwilling to obtain all of the information we would need to make fair judgments about people or situations. In the absence of the "total picture," stereotypes in many cases allow us to "fill in the blanks."... Free Essays on Criminal Free Essays on Criminal Deep within the word, â€Å"American† is its association with Race. To identify someone as Hispanic is to say very little, we need the adjective â€Å"white† or â€Å"Latino† or â€Å"colored† to make our meaning clear. In this country it’s the reverse. American means white and that’s it, and Latinos struggle to make the term applicable to themselves hyphen after hyphen and so on. Because American means white, those who are not white are presumed to be recent arrivals and often told to â€Å"go back to where they came from.† Thus we appear to operate within the dichotomized racial categories of American/non-American; these are racial categories, because they effectively mean white/nonwhite (17). This is the reason why I believe race in the United States has indeed been socially constructed is through stereotypes and lack of knowledge. The comparison between â€Å"whites† and â€Å"Latinos† are very different and how each of the group is perceived is very different. A "stereotype" is a generalization about a person or group of persons. We develop stereotypes when we are unable or unwilling to obtain all of the information we would need to make fair judgments about people or situations. In the absence of the "total picture," stereotypes in many cases allow us to "fill in the blanks."...

Comparative Advantage Essays

Comparative Advantage Essays Comparative Advantage Essay Comparative Advantage Essay I have chosen the Comparative Advantage Theory for my key term to discuss. I chose this term because it has a great importance on world trade clearly help shape the pattern of world trade, and also to get a better understanding of the concept. Comparative Advantage is the benefit or advantage of an economy to be able to produce a commodity at a lesser opportunity cost. According to Stalemate (2009), opportunity cost is the value of what had to be given up, or forgone, to consume or achieve the object. This term simply meaner, countries should specialize in a certain lass of products for export, but import the rest of product even if the country holds an absolute advantage in all products. The scholarly article I chose this week to discuss is, State should target sectors where the country industry has a comparative advantage written by T. T Ram Moan. The article talks about Justine Hussy Lines book titled The Quest for Prosperity. The book attempts to give solutions to the world financial crisis. In the article he talks about Lines distinguishes between advanced nations and developing ones in the short-run, and how money stimulus ill be effective for developing nations and not advanced nations, and also discuses Lines perspectives for Long-term growth. According to the article, government must identify the right growth sectors and support investment in those sectors, because it will lead to the overall growth in that economy. A key example is what Singapore did in the sasss when they focused on specialty chemicals that resulted in drawing developed nations into their economy (Moan, 2012). This seems pretty easy but has failed in many nations because it is hard to sometimes identify the sectors that truly eve Comparative Advantage in an economy. The theory encourages nations to engage in true free trade and to specialize in areas where they can be very effective and efficient at lower cost, instead of looking to bolster weak industries from foreign competition by imposing protective tariffs that otherwise stifle the production that leads to overall gains in wealth. Even though this theory has a huge advantage on global trade, it does have its flaws, which includes the following: It may overstate the benefits of specialization by ignoring certain costs. These costs include transport costs and any external costs associated with trade, such as air and sea pollution. Also it does not take into account relative prices and exchange rates, and also assumes perfect mobility of factors without any diminishing returns. Furthermore, complete specialization might create structural unemployment as some workers cannot transfer from one sector to another.

Human Resource Management Essay Example | Topics and Well Written Essays - 1750 words

Human Resource Management - Essay Example According to the research findings the success of any organization depends on its human resource. Motivated human resource would strive to meet the goals of the organization while demoralized employees would conduct their duties in a clumsy manner. Every organization has to be sensitive to the human resource department because it is the motor engine of an organization. When human resource of an organization fails, the success of the organization is at stake. This means that the department must work in conjunction with other departments to realize the set goals and objectives. Developing appropriate policies in an organization motivates and provides an opportunity for employees of an organization to gain promotion. Australian company ninemsn provide a wide range of services to its clients in media practice. The company offers the following services to its customers, publishing of Magazine and TV brands, MSN online services, news Websites; Web based email services, entertainment among others. It also offers information in many fields such as health, business, lifestyle, shopping and travel among others. The company products attract large number of customers thereby influencing the number of workers that the company has to employ in order to meet the need of its customers. The labor force of the company includes IT technicians, sales executives, accountants, customer care executives, directors among others. Such labor force requires comprehensive human resource planning and management in order for the company to meet its goals. Scope ninemsn Company offers media services in Australia and beyond. This report focuses on human resource department of the organization. Methodology This report intends extracts company information from company website, on line information and newspapers. The aim is to identify internal human

Contract and Event Management Essay Example | Topics and Well Written Essays - 2000 words

Contract and Event Management - Essay Example The contracts are typically arranged to ensure finest food quality services in the event. There are different types of contracts. The catering contracts for event management sectors will help in saving time and money. Thus, planning the arrangements effectively will help in thriving in the catering business. Remember, an event cannot take place without food (Bode, 2003). Food is important in any event. Hence, adequate planning of providing food in the events by tying up with event management firm is likely to boost the company’s revenue earning. To start with such business plan, you must have some basic knowledge about the food industry and you must posses and urge to give the best service to your client. Offering quality services is the key to succeed in the food industry. Efficiency and preparing tasty dishes will help in gaining quick popularity in the domain. Now, flexibility is essential, as depending on the nature of the product some will order for daily services. Thus, service enhancement is essential (Hayes and Ninemeier, 2012). To maintain consistency in the food preparation the caterer will require good products from the market. Besides, cooking finest dishes and delivering the products on daily basis, the caterer should develop a very good relationship with the supplier. Supplier and caterer must hold a good partnership, as you will require quality product to offer quality services in the catering domain. Creativity and innovation is the key to succeed in this industry (Hayes and Ninemeier, 2012). Thus, the contractor will contact only the dynamic item providers who can supply innovative products to deliver special services in the outlets. The firm should begin with a strategic planning procedure. Now to go about the process, analyze the business in relation to the below mentioned ideas; identification if the idea of the contract fits the