DataMatrix Generation In .NET
Using Barcode creation for VS .NET Control to generate, create ECC200 image in VS .NET applications.
Decode DataMatrix In .NET
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
FIGURE 1152:
Barcode Creator In Visual Studio .NET
Using Barcode encoder for .NET Control to generate, create barcode image in VS .NET applications.
Barcode Recognizer In .NET Framework
Using Barcode decoder for .NET Control to read, scan read, scan image in VS .NET applications.
General landscape of
DataMatrix Maker In Visual C#.NET
Using Barcode encoder for .NET Control to generate, create DataMatrix image in .NET applications.
Generate Data Matrix ECC200 In .NET Framework
Using Barcode generator for ASP.NET Control to generate, create Data Matrix 2d barcode image in ASP.NET applications.
DataMatrix Generation In VB.NET
Using Barcode encoder for .NET Control to generate, create Data Matrix 2d barcode image in Visual Studio .NET applications.
Drawing Matrix 2D Barcode In .NET
Using Barcode maker for .NET Control to generate, create Matrix 2D Barcode image in .NET applications.
range When carbons of any type (sp, sp2, sp3) are attached to electronegative elements, a down eld shift occurs Thus, aliphatics are moved into the 50 100 ppm region, acetylenics (nitriles) are moved into the 100 150 range, and ole nics (carbonyls) migrate to the 150 200 ppm region The combination of this wide landscape with the sharp singlet signals means that every unique carbon in a molecule usually can be resolved in a 13C spectrum This is useful because it can reveal important information about symmetry within a molecule For example, 2-nitroaniline and 3-nitroaniline (Figure 1153) exhibit 6 carbon peaks, as we would expect However, 4-nitroaniline only has 4 carbon signals because of its inherent symmetry
Encoding Code 39 Extended In .NET
Using Barcode creator for Visual Studio .NET Control to generate, create Code 39 image in .NET applications.
EAN13 Generator In .NET Framework
Using Barcode creation for Visual Studio .NET Control to generate, create European Article Number 13 image in .NET applications.
Bar Code Generation In Visual Studio .NET
Using Barcode creation for .NET Control to generate, create bar code image in .NET framework applications.
Drawing British Royal Mail 4-State Customer Code In VS .NET
Using Barcode drawer for .NET Control to generate, create RM4SCC image in Visual Studio .NET applications.
NO2 NO2 6 carbon peaks
GTIN - 128 Generation In None
Using Barcode printer for Word Control to generate, create USS-128 image in Office Word applications.
Recognizing Bar Code In Visual Basic .NET
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in VS .NET applications.
FIGURE 1153:
Data Matrix ECC200 Printer In Objective-C
Using Barcode maker for iPhone Control to generate, create ECC200 image in iPhone applications.
EAN 128 Recognizer In Visual C#
Using Barcode decoder for .NET Control to read, scan read, scan image in .NET framework applications.
6 carbon peaks
EAN13 Creator In Java
Using Barcode creator for Java Control to generate, create EAN13 image in Java applications.
GS1-128 Maker In None
Using Barcode generation for Software Control to generate, create UCC.EAN - 128 image in Software applications.
4 carbon peaks
Printing Code 3/9 In Java
Using Barcode drawer for Java Control to generate, create Code39 image in Java applications.
Make GS1 128 In Java
Using Barcode maker for Java Control to generate, create GS1 128 image in Java applications.
Impact of symmetry on 13C NMR spectrum
Organic Chemistry
1 Bonding The most common bonds found in organic chemistry are: Covalent bonds between atoms of very similar electronegativity Polar covalent bonds between atoms of moderately differing electronegativity Ionic bonds between atoms of vastly differing electronegativity in their ionic form The connectivity of bonds in molecules can be shown by Lewis structures, which sometimes are depicted using multiple resonance forms These forms are evaluated using the following criteria: Each atom should have an octet of electrons (although fewer are possible) No row 2 atom can have more than an octet Structures should minimize charge separation Charge separation should follow electronegativity 2 Molecular Shape The shape of a molecule is ultimately driven by the central atom geometry at each atomic center, which in turn is determined by atomic orbital hybridization For carbon, these are: sp hybridization, which results in linear geometry and 180 bond angles sp2 hybridization, which results in trigonal planar geometry and 120 bond angles sp3 hybridization, which results in tetrahedral geometry and 1094 bond angles When a tetrahedral center is surrounded by four unique groups, the center is said to be an asymmetric center (or stereocenter) Compounds with asymmetric centers are almost always chiral (or handed), and they exist as two enantiomers (or nonsuperimposable mirror images) Molecules can adopt many conformations (relative arrangements of atoms or groups), which are usually rapidly interconverting For open-chain compounds (such as butane), the most important conformations are staggered (most stable) and eclipsed (least stable) In staggered conformations, substituents on adjacent atoms that are farthest from each other are said to be antiperiplanar; those that are next to each other are gauche In eclipsed conformations, all substituents are eclipsed 3 Electronic Structure Atomic orbitals are combined by the method of linear combination of atomic orbitals (LCAO) to form new molecular orbitals (MOs) The number of molecular orbitals obtained is equal to the number of atomic orbitals used to make them Usually, there are an equal number of bonding orbitals (of lower energy than disconnected atoms) and antibonding orbitals (of higher energy than disconnected atoms) When bonds are next to each other in a 1,3-relationship, they form extended systems, in which the bonds are said to be conjugated These conjugated systems form molecular orbitals that are easily predictable from the combination of adjacent p orbitals In general, conjugated bonds are more stable than nonconjugated ones The MO description of conjugated systems offers a fuller understanding of Lewis resonance forms
Certain cyclic conjugated bonds can form aromatic systems To be aromatic, a molecule must have a cyclic, contiguous, and coplanar array of p orbitals Systems that do not ful ll all of these criteria are considered nonaromatic For those that do satisfy all three conditions, H ckel s Rule states that aromatic systems must contain (4n + 2) electrons, whereas those that contain 4n electrons are considered antiaromatic Aromatic and conjugated systems can be affected by attached substituents Generally speaking, substituents are classi ed as either electron-donating groups (EDG), such as amino and methoxy, or electron-withdrawing groups (EWG), such as nitro and cyano The impact can be broken down into inductive effects, which arise from electronegativity differences and are communicated through bonds, and resonance effects, in which electron density is moved across extended systems 4 Nomenclature The IUPAC nomenclature of organic compounds is driven by consideration of the carbon backbone and functional groups The process starts by determining the identity of the parent compound, which is de ned as the longest possible carbon chain bearing the highest order functional group Once the parent compound is de ned, all other groups become substituents Substituents can be simple (methyl, ethyl, etc) or compound (such as 2,2-dimethylpropyl) When numbering a compound substituent, the point of attachment is always considered carbon 1 The conversion of alkane chains into substituents is simple: methane becomes methyl However, functional groups are more subtle: an alkanol becomes a hydroxalkyl substituent, and an alkanone becomes an oxoalkyl substituent Chiral centers are named using the Cahn-Ingold-Prelog (CIP) rules of priority: prioritize atoms around an asymmetric center according to atomic number orient the center so that the lowest-priority atom is farthest away if the priority of the remaining atoms proceeds clockwise from highest to lowest, then it is an R center if the priority of the remaining atoms proceeds counterclockwise from highest to lowest, then it is an S center The CIP rules are also used to specify the geometry around double bonds Here the methodology is as follows: orient the double bond so that it is horizontal on each side, label the two substituents according to their CIP priority if the two top-priority substituents are pointing in the same direction, it is a Z alkene if the two top-priority substituents are oriented opposite each other, it is an E alkene 5 Reaction mechanisms Reactions generally fall into the following classi cations: radical reactions, characterized by unpaired electrons polar chemistry, in which charged species are involved, and pericyclic chemistry, which involves concerted electron motion without development of charge separation These reactions can be used for synthetic methodology, which involves the two major techniques of carbon-carbon bond formation and functional group transformation Methods can be organized by the preparation of and reactions of various functional groups
6 Isolation and characterization Once compounds have been made, they must be puri ed and identi ed The major separation techniques used in the organic laboratory are: Extraction, including aqueous workup, which is based on differential solubility Chromatography, which depends upon differential af nity to mobile and stationary phases Distillation and sublimation, in which separation occurs based on differential volatility Recrystallization, which relies on differential solubility Separation techniques can be used both for preparative puri cation and analysis Methods for identifying compounds include: Combustion analysis, which can be used to obtain an empirical formula UV-Vis spectroscopy, which reveals the nature of extended systems through electronic transitions Mass spectrometry, which can provide information about molecular weight through charge to mass ratios Infrared spectroscopy, which indicates the presence or absence of functional groups through molecular vibrations Nuclear magnetic resonance, which provides data about the topography of molecules through spin ips of protons and carbons 7 Proton NMR Nuclear magnetic resonance (NMR) arises from the absorption of energy in a nuclear spin ip, a transition that is extremely sensitive to the electronic density around it The position of an NMR signal relative to the internal standard TMS is called the chemical shift, and these data reveal the nature of a proton s chemical environment Protons that resonate at much higher frequency than TMS are said to be down eld, and those that appear close to the standard are said to be up eld A down eld shift is indicative of an electron-de cient (or deshielded) environment, usually caused by the proximity of an electron-withdrawing group (EWG) The integration of NMR signals is used to calculate the ratio of the respective protons The typical range for a proton NMR spectrum is 0 10 ppm, and this can be divided into the following general categories: 0 to ca 25 ppm: aliphatic and and alkynyl C-H protons ca 25 to ca 5 ppm: aliphatic C-H protons where carbon is attached to an electronegative element ca 5 to ca 65 ppm: alkenyl (sp2) C-H protons ca 65 to ca 9 ppm: aromatic (sp2) C-H protons ca 10 ppm: aldehydic C-H protons In addition, signals often exhibit splitting patterns, many of which can be interpreted using the n 1 rule, which states that the multiplicity corresponds to the total number of adjacent protons plus one Thus, a proton with only one next-door proton would give rise to a doublet, and so on This phenomenon of scalar splitting is a through-bond effect communicated by the backbone The magnitude of the splitting (otherwise known as the coupling constant or J-value) is also diagnostic Freely rotating systems usually exhibit a J-value of about 7 Hz; however, this value can be different in constrained systems such as cycloalkanes 8 Carbon NMR Carbon NMR is based on the same principle as proton NMR However, carbon signals are spread across a wider span than proton absorbances (ca 200 ppm vs
10 ppm) Furthermore, since only carbon-13 is observed by NMR, and its natural abundance is about 1%, practically no carbon-carbon splitting is observed Carbon does couple with hydrogen, but this coupling is arti cially suppressed by off-resonance decoupling Consequently, each carbon signal shows up as a singlet, and each unique carbon can usually be resolved For this reason, carbon NMR is very useful in identifying symmetry within a molecule In other words, if the molecular formula indicates the presence of ten carbon atoms, but the NMR only reveals nine signals, this is strong evidence that a pair of carbon atoms are related by symmetry Like proton NMR, chemical shift can also provide important information In very general terms, the carbon NMR spectrum can be divided into four regions: 0 to ca 50 ppm: aliphatic (sp3) carbons ca 50 to ca 100 ppm: sp3 carbons attached to heteroatoms; alkynyl (sp) carbons ca 100 to ca 150 ppm: aromatic and ole nic (sp2) carbons; nitrile (sp) carbons ca 150 to ca 200 ppm: carbonyl carbons
Copyright © . All rights reserved.