Retention of configuration is observed in

The S N2 mechanism There are two mechanistic models for how an alkyl halide can undergo nucleophilic substitution. In the first picture, the reaction takes place in a single step, and bond-forming and bond-breaking occur simultaneously. (In all figures in this section, 'X' indicates a halogen substituent). This is called an ' S N2' mechanism. In the term S N2, S stands for 'substitution', the subscript N stands for 'nucleophilic', and the number 2 refers to the fact that this is a bimolecular reaction: the overall rate depends on a step in which two separate molecules (the nucleophile and the electrophile) collide. A potential energy diagram for this reaction shows the transition state (TS) as the highest point on the pathway from reactants to products. If you look carefully at the progress of the S N2 reaction, you will realize something very important about the outcome. The nucleophile, being an electron-rich species, must attack the electrophilic carbon from the back side relative to the location of the leaving group. Approach from the front side simply doesn't work: the leaving group - which is also an electron-rich group - blocks the way. The result of this backside attack is that the stereochemical configuration at the central carbon inverts as the reaction proceeds. In a sense, the molecule is turned inside out. At the transition state, the electrophilic carbon and the three 'R' substituents all lie on the same plane. What this means is that S N2 reactions whether e...

The synthesis of three bridgehead homocuneanes acetates viz 1-bromopentacyclo [4.3.0.0 2.4.0 3.8.0 5.7]nonan-9-one ethylene ketal 4-acetate ( 10), 1-bromopentacyclo[4.3.0.0 2.4.0 3.8.0 5.7]nonane 4-acctate ( 22) and pentacyclo[4.3.0.0 2.4.0 3.8.0 5.7]nonane-9-one ethylene ketal 4-acetate ( 31) is described, starting from the readely available homocubane carboxylic acid ( 4). The base and acid catalyzed homoketonization reaction of these acetates has been studied. Under basic conditions the acetates ( 10, 22 and 31) are converted into tettacyclo[4.3.0.0 2.4.0 3.8]nonane derivatives by a cyclopropanol ring cleavage. This homoketonization reaction is a stereospecific process proceeding with retention of configuration. The effect of cage strain on the stereochemistry of base induced homoketonization of bridgehead cage alcohols is discussed. The acid catalyzed homoketonization of acetate ( 10) was also found to occur exclusively with retention of configuration. • Trials in children with chronic kidney disease do not consistently report outcomes that are critically important to patients and caregivers. This can diminish the relevance and reliability of evidence for decision making, limiting the implementation of results into practice and policy. As part of the Standardized Outcomes in Nephrology—Children and Adolescents (SONG-Kids) initiative, we convened 2 consensus workshops in San Diego, California (7 patients, 24 caregivers, 43 health professionals) and Melbourne, Australia ...

In this article, we will explore five common Google Analytics 4 mistakes that can easily happen and provide practical tips to avoid them. 1. Not Setting Data Retention Period GA4 comes with a two-month data retention period by default, and you have the option to set it to 14 months. The retention period is applied to custom reports in explorations, whereas data in the standard reports never expire. Once the retention period has passed, data will be automatically deleted – which means if you don’t change that setting as you set up GA4, you will not be able to run YoY custom reports and will lose valuable historical data. In order to change the retention period, navigate to Data Settings> Date Retention, and in the dropdown, choose 14 months. In other words, each time a user engages in a new activity, their data retention period gets extended for another 14 months. Honestly, I can’t think of a use case when you would choose to turn that option off, so I keep it switched on. 2. Dimensions With High Cardinality High-cardinality dimensions are dimensions that contain more than 500 unique values within a single day. This can present challenges and limitations in data analysis within GA4. Cardinality in GA4 can negatively affect data accuracy and reliability. For example, when you track the exact word count as a custom dimension on every article page, you may end up having high cardinality if you have thousands of articles because the word count can be different for every article...

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