The substitution reactions

The substitution reactions Acknowledgement The preparation of this project on the topic- substitution reactions.: a profile would not have been possible without the valuable contribution of my TEACHERS. I would like to give most specially thanks to my CHE sir Dr. Ashish kumar who is my chemistry teacher to giving me the important guidelines during making this project. So, I hope this project will provide large and sufficient information about the different coordination numbers present in the coordination chemistry. Introduction In substitution reaction, afunctional groupin a particularchemical compoundis replaced by another group[1]. Inorganic chemistry, theelectrophilicandnucleophilicsubstitution reactions are of prime importance. Organic substitution reactions classified in several mainorganic reactiontypes depending on whether thereagentthat brings about the substitution is considered anelectrophileor anucleophile, whether areactive intermediateinvolved in the reaction is acarbocation, acarbanionor afree radicalor whether thesubstrateisaliphaticor aromatic. It also is helpful for optimizing a reaction with regard to variables such as temperature and choice of solvent Substitution reaction : chlorination of methane Nuclophilic reactions: These kind of substitution reactions happen when the reagent is a nucleophile, which means, an atom or molecule with free electrons. Anucleophilereacts with analiphaticsubstrate in anucleophilic aliphatic substitutionreaction. When the substrate is anaromaticcompound the reaction type isnucleophilic aromatic substitution. Carboxylic acidderivatives react with nucleophiles innucleophilic acyl substitution. This kind of reaction can be useful in preparing compounds The Nucleophilic substitutions can be produced by two different mechanisms: Monomolecular nucleophilic substitution (SN1): In this case the reaction proceeds in stages, the compounds first dissociate in their ions and then this ions react between them. Its produced by carbocations. Bimolecular nucleophilic substitution (SN2): In this case the reaction proceeds in only one stage. The attack of the reagent and the expulsion of the leaving group happen simultaneously. Electrophilic reaction Electrophilesare involved inelectrophilic substitutionreactions and particularly inelectrophilic aromatic substitutions: Electrophilic reactions to other unsaturated compounds thanarenesgenerally lead toelectrophilic additionrather than substitution. Radical substitutions Aradical substitutionreaction involvesradicals The term nucleophile comes from the Greek meaning nucleus loving, in other words nucleophiles seek positive charged centres. Nucleophiles have lone pairs of electrons and may carry a negative charge. There are many examples of nucleophiles, such asNH3,H2O,CN-,HC?C-, andOH-. Alkyl halides contain a halogen (X =F,Cl,BrorI) covalently bonded to a carbon atom. Due to the electronegativity differences between carbon and the halide, theC-Xbond is polar with a partial positive charge (?+) on the carbon atom and a partial negative charge (?-) on the halogen. Halogens are good leaving groups and can be replaced by an incoming nucleophile. Nucleophilic substitution is the reaction of an electron pair donor (the nucleophile, Nu) with an electron pair acceptor (the electrophile). An sp3-hybridized electrophile must have a leaving group (X) in order for the reaction to take place. Mechanism of Nucleophilic Substitution The term SN2 means that two molecules are involved in the actual transition state: The departure of the leaving group occurs simultaneously with the backside attack by the nucleophile. The SN2 reaction thus leads to a predictable configuration of the stereocenter it proceeds with inversion (reversal of the configuration). In the SN1 reaction, a planar carbenium ion is formed first, which then reacts further with the nucleophile. Since the nucleophile is free to attack from either side, this reaction is associated with racemization. In both reactions, the nucleophile competes with the leaving group. Because of this, one must realize what properties a leaving group should have, and what constitutes a good nucleophile. For this reason, it is worthwhile to know which factors will determine whether a reaction follows an SN1 or SN2 pathway. Common examples include Organic reductionswithhydrides, for example R-X?R-HusingLiAlH4 (SN2) hydrolysisreactions such as R-Br + OH-?R-OH+Br-(SN2) or R-Br + H2O ? R-OH +HBr (SN1) Williamson ether synthesis R-Br +OR-?R-OR+ Br- (SN2) Electrophilic substitution Electrophilic aromatic substitutionorEASis anorganic reactionin which an atom, usuallyhydrogen, appended to anaromatic systemis replaced by anelectrophile. The most important reactions of this type that take place arearomatic nitration,aromatic halogenation,aromatic sulfonation, and acylation and alkylatingFriedel-Crafts reactions. Basic reaction Aromatic nitrationsto formnitro compoundstake place by generating a nitronium ion fromnitric acidandsulfuric acid. Aromatic sulfonationofbenzenewith fumingsulfuric acidgives benzenesulfonic acid. Aromatic halogenationof benzene withbromine,chlorineoriodinegives the corresponding aryl halogen compounds catalyzed by the corresponding iron trihalide. TheFriedel-Crafts reactionexists as anacylationand analkylationwith acyl halides oralkyl halidesas reactants. The catalyst is most typicallyaluminium trichloride, but almost any strongLewis acidcan be used. In Fridel-Crafts acylation, a full measure of aluminium trichloride must be used, as opposed to a catalytic amount. Basic reaction mechanism In the first step of thereaction mechanismfor this reaction, the electron-rich aromatic ring which in the simplest case isbenzeneattacks the electrophileA. This leads to the formation of a positively-charged cyclohexadienylcation, also known as anarenium ion. Thiscarbocationis unstable, owing both to the positive charge on the molecule and to the temporary loss ofaromaticity. However, the cyclohexadienyl cation is partially stabilized byresonance, which allows the positive charge to be distributed over three carbon atoms. In the second stage of the reaction, aLewis baseBdonates electrons to the hydrogen atom at the point of electrophilic attack, and the electrons shared by the hydrogen return to thepisystem, restoring aromaticity. An electrophilic substitution reaction on benzene does not always result in monosubstitution. While electrophilic substituents usually withdraw electrons from the aromatic ring and thus deactivate it against further reaction, a sufficiently strong electrophile can perform a second or even a third substitution. This is especially the case with the use ofcatalysts. Radical Substitution Radicals A radical is a species that contains unpaired electrons. Typically formed by a homolytic bond cleavage as represented by the fishhook curved arrows: RADICAL CHAIN MECHANISM FOR REACTION OF METHANE WITH Br2 Step 1 (Initiation) Heat or uv light cause the weak halogen bond to undergo homolytic cleavage to generate two bromine radicals and starting the chain process. Step 2 (Propagation) A bromine radical abstracts a hydrogen to form HBr and a methyl radical, then The methyl radical abstracts a bromine atom from another molecule of Br2to form the methyl bromide product andanotherbromine radical, which can then itself undergo reaction 2(a) creating a cycle that can repeat. Step 3 (Termination) Various reactions between the possible pairs of radicals allow for the formation of ethane, Br2or the product, methyl bromide. These reactions remove radicals and do not perpetuate the cycle. There are two components to understanding the selectivity of radical halogenations of alkanes: reactivity of R-H system reactivity of X. R-H The strength of the R-H varies slightly depending on whether the H is 1o, 2oor 3o. The following table shows the bond dissociation energy, that is the energy required to break the bond in a homolytic fashion, generating R.and H. Halogen radical, X. Bromine radicals are less reactive than chlorine radicals Br.tends to be more selective in its reactions, and prefers to react with the weaker R-H bonds. The more reactive chlorine radical is less discriminating in what it reacts with. The selectivity of the radical reactions can be predicted mathematically based on a combination of an experimentally determined reactivity factor, Ri, and a statistical factor, nHi. In order to use the equation shown below we need to look at our original alkane and look at each H in turn to see what product it would give if it were to be susbtituted. This is an exercise in recognizing different types of hydrogen, something that will be important later. REFERENCES:- Chang Raymond www.wikepedia.org www.google.com

Brain Development Essay

At birth there are about 100 billion brain cells produced and they are beginning to connect with each other. At the first week of age, brain development starts with conception. It is important to reach the age of an infant and practice the ten principals. In the early years, young brains produce almost twice as many synapses as they will need. By age two, the number of synapses a toddler has is similar to that of an adult. By three the child has twice as many synapses as an adult. The infant brain develops through the interaction with the world around, especially the interaction with adults. At the first few months, an infant cannot response to praise or punishment. Emerging research on brain development indicates that the degree for responsive care giving that children receive as infants and toddlers positively affects the connections between neurons in the brain (Brain Cells), and the architecture of the brain itself. The first three years of life are the period of growth in all areas of a baby’s development. Consistent, responsive relationships enable infants and toddlers to develop secure attachments. Infants and Toddlers develop knowing and understanding by perceiving experiences directly with the senses. For infants to acquire the ability to comprehend this sensory information they must b able to distinguish between the familiar and the unknown; later they will begin to consider, to formulate, and to form mental images in this process of experiencing and clarifying the environment. Infants begin by exploring the world with their bodies. They internalize what they take in through their senses and display it in their physical movements. Infants gather vital information through such simple acts as mouthing, grasping, and reaching. The knowing process also involves language abilities. As young children use their senses to experience the world, they need labels to categorize and remember these experiences. By creating these labels, children increase their ability to communicate and begin to control their own behavior. These expanded abilities give young children additional opportunities to understand the world (Infant, Toddlers, and Caregiver Ninth Edition). Recent brain research supports the goal of building a total person instead of concentrating on cognitive development alone. Providing a rich environment with interesting things to do is desirable and stimulates cognitive development. But that does not work without working on physical, social, and emotional development at the same time. What make differences are the day-to-day living, the relationships, the experiences, the diapering, the feedings, the toilet training, and the free play and exploration that contribute to intellectual development. Early experiences matter, and shape brain architecture. Advances in brain research have provided great insight into how young children’s experiences have profound impact on genetic predispositions and thereby share the processes that determine whether their brains will have adaptations or maladaptations for later learning, memory, reasoning, executive functioning, expressing a full range of positive and negative emotions, socialization, behavior control and lifelong health. The thrust of this element is to close the gap between what we have learned and what we do with infants and toddlers. Experiences that prepare the developing brain to function optimally include having warm, nurturing, attentive social interactions and conscientiously buffering young children from the adverse impact of toxic stress. Lack of these kinds of experiences can have devastating, long-term effects on brain development including cognitive functioning and social-emotional competencies. For example, unpredictable or chaotic routines or lack of consistent caregivers may jeopardize children’s foundation for identity development or self regulation, or few language experiences, toys, and opportunities to explore impede the development of neural connections and pathways that facilitate learning (Essential elements of Quality-Infant-toddler Program). To deliver high quality care giving, adults need to understand and recognize key developmental processes that help them understand and support infants and toddlers. Since this essential element explicitly identifies knowledge about key developmental processes threats to them as a factor in quality infant-toddler program, three terms are defined as important pieces of a wider knowledge base about brain development that informs practice: serve and return, executive functioning and toxic stress. Serve and return is the interaction between young children and their parents and caregiver is a key to healthy brain development. It helps to create neural connections that build later cognitive and emotional skills. Executive functioning represents the cognitive skills that enable a child to focus on, hold, and think about information, filter distractions; and divert their attention to something new. The foundation for executive functioning is laid in infancy and is facilitated through early experiences. Acquiring the early building blocks of (executive functioning) skills is one of the most important and challenging tasks of the early childhood years. Toxic stress is defined as strong, frequent, and/or prolonged adversity without adequate adult support. Toxic stress disrupts brain development. While some experience with manageable stress is important for healthy development, prolonged, uninterrupted, overwhelming stress; toxic stress without the buffering relationships a child needs, can result in damaged, weakened systems and brain architecture that can have negative long-term effect (Essential Elements of Quality-Infant-Toddler Program). Environments make a difference in brain development. Environments that provide proper nutrition and regularly scheduled periods of sleep and physical activity consistently promote warm, nurturing, attentive social interaction; and conscientiously buffer young children from the adverse impacts of toxic stress. Lack of adequate nutrition, physical activity, appropriate sensory stimulation or social-emotional developmental experiences disrupt brain architecture and can have a decisively negative Impact on future development (Essential Elements of Quality-Infant-Toddler Program). Finding about the impact of early experiences on brain development highlight the importance of intervening early with highly stressed infants and toddlers and their families. Infants and children who are rarely spoken to, who are exposed to few toys, and who have little opportunity to explore and experiment with their environment may fail to fully develop the neural connections and path ways that facilitate later learning. Despite their normal genetic endowment, these children are at a significant intellectual disadvantage and are likely to require costly special education or other remedial services when they enter school. Fortunately, intervention programs that start working with children and their families at birth or even prenatally can help prevent this tragic loss of potential. While high-quality infant and toddler programs are not necessarily intervention programs. When caregiver and parenting practices are grounded in knowledge of early brain development, caregivers and parents are much more effective in providing experiences that facilitate optimal development including strong brain architecture (Essential element of Quality-Infant-Toddler Program).

Ethical and Governance Issues Raised - 3252 Words

Table of Contents 1 Introduction 2 2 Discussion of case study 2 2.1 Identification of the Ethical and Governance issues raised in the case study 2 2.2 Critical analysis of the main ethical and the governance issues raised in the case study 5 2.3 An evaluation of the conditions that enabled the issues identified to arise 7 2.4 Recommendations to the company 9 3 Conclusion 11 4 References 12 Introduction Apple is one of the most successful companies to date, they have dominated most of the markets they have entered, and all of this was able to become a reality because of Steve Jobs, the founder of Apple. He is seen as a somewhat genius when it comes to business, and his employees seem to be very satisfied, but what most people†¦show more content†¦corporate social responsibility; and (2) what has Apple actually done in regards to ensuring that its Chinese suppliers comply with Apple’s values. Corporations such as Apple, are constantly under pressure to maximise shareholder wealth, as shareholders are the ultimate owners of the company. A key proponent of this view was Nobel-Prize winning economist, Milton Friedman. Friedman states in a New York Times article (1962) that managers’ key responsibility as agents was to the act in shareholders’ best interests; this was management’s social responsibility. By acting in the interest of others, such as the interest of society, management are not fulfilling their duty to shareholders and are effectively imposing a tax on shareholders, who could more efficiently allocate their resources to this purpose rather than rely on corporations. However, modern theory known as corporate social responsibility (CSR), has complicated the situation in that stating that companies are not only responsible to its shareholders, but also to the stakeholders which its actions may impact (Freeman 1984). While this may seem to contradict the mantra of profit maximisation, Russo and Perrini (2010) suggest that in today’s conscience-minded society, success is based not only on maximising profit but also on a corporation’s stakeholder relationships, which include social and environmental issues. The important factor in understanding CSR is that organisationsShow MoreRelatedFinancial Management And Corporate Social Responsibility1216 Words   |  5 Pagesworld these days as well as the significant growth of organization, there are such key concerns on not only the issue of financial management or corporate social responsibility, but also the importance of ethics and governance, in which how an organization manages its business acting in the best interests of public and stakeholders. 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Idioms and Expressions With Do

The following idioms and expressions use the verb do. Each idiom or expression has a definition and two example sentences to help understanding of these common idiomatic expressions with do.   Do a Double Take Definition: look twice at someone or something because you are surprised She did a double take when he walked into the room.Did you see that man do a double take as he looked at the price? Do a Number on Someone Definition: trick someone, cheat someone, hurt someone very badly Im afraid she did a number on him when she broke up.That guy did a number on John to the tune of $500! Do an About Face Definition: turn around, return to where someone came from Id like you to do an about face and go clean your room!As soon as I got to work I realized Id have to do an about face because Id left my briefcase at home. Do Away With Something Definition: prohibit something, make something not available   They tried to do away with coffee in some cultures to little success.Anytime they do away with something people want it even more.   Do Justice to Something Definition: do successfully and with honor, complete in a befitting manner I think that painting doesnt do justice to him.Alice really did justice to the presentation.   Do One’s Duty Definition: complete a responsibility, do something that is expected of you Remember to do your duty by honoring your parents.Ill do my duty but nothing more. Do Ones Part Definition: do something that is required of you, join in doing something that requires many people He feels that volunteering is doing his part.Do you part and get along and youll have no problems here. Do or Die Definition: complete a task or utterly fail Its do or die time now. Were getting married!Well John, its do or die. Lets go! Do Someone Good   Definition: be beneficial for someone I think taking the week off will do you good.She told me a massage would do me good.   Do Something Over Definition: repeat an action often because of a poor start Lets do that over! I wasnt concentrated enough!Id love to do college over if I had the chance. Do Someone Proud definition: do something so well that another person is proud of you David did his father proud throughout his successful life.I think youll do your family proud this year.   Do Someones Heart Good Definition: be good for someone emotionally I think listening to some classical music would do your heat good.Getting straight As did her heart good. Do Something by Hand Definition: build something on ones own He built his house by hand.I created that desk by hand.   Do Something in Vain Definition: do something with no reason or chance at success Peter feels his doing the job in vain.Never feel youre doing something in vain. Theres always a reason. Do Something on the Fly Definition: do something quickly without thinking I did it on the fly, its nothing special.Lets do it on the fly. It wont take long. Do Something on the Run Definition: do something while on the way to somewhere else We did it on the run while on the way to Arizona.You can do it on the run. Lets go! Do Something on the Sly Definition: do something without having other people notice She did it on the sly. Her husband never had a clue.He made lots of money by doing it on the sly. Do the Honors Definition: do something like cutting a cake, or giving a speech that is an honor Id like to let your father do the honors.Ill do the honors and toast to happy and long life! Do the Trick definition: complete the task, function as a solution I think this pen will do the trick.Youll come up with something to do the trick. Do You Read Me? Definition: question asked usually in a stern manner to ask if someone understands Well have no more talk! Do you read me?!Thats enough. Do you read me?