 Today we are going to discuss about a new spectroscopic technique that is called infrared spectroscopy infrared spectroscopy is part of these the advanced chemical spectroscopic techniques which are used to determine different kinds of chemical information starting from the electronic transition to the vibrational spectroscopy to even the nuclear transitions. So this normally used in the machines as a Fourier transform in per spectroscopy or something known as FTIR so FTIR is the is the major Fourier transform technique which is normally used in the experiments and whenever you go to any research labs they will talk about FTIR the full form FTR is Fourier transform infrared spectroscopy basically is an infrared spectroscopy but the information which are obtained from the machine are basically plotted in this Fourier space instead of the real space and Fourier space is nothing but the wave number space. Now this is this spectroscopic technique rather infrared spectroscopic techniques it deals with the infrared region of the electromagnetic spectrum and I will first give you an idea what is infrared radiation is now as you know infrared radiation is lies between visible and the microwave portions of the electromagnetic spectrum in the very first class I just showed you the detail in for its the little spectrum of the electromagnetic radiation where starting form X rays or gamma rays to radio waves are shown and whether UV and visible comes in the middle of the of the spectrum. So infrared which comes between the visible and the microwave that is this one here so you can see this is the part visible microwave we have already discussed about the UV and the visible spectroscopy in the last class. So here the wavelength comes basically falls between these two the spectrums infrared normally have higher wavelengths than the visibles as clear your blends increases in this direction so the lambda increase in this direction and the frequency of it decreases as you go from UV to microwave radio infrared in since region I basically divided into three parts one is of mid infrared that is exactly the infrared radiation region and then you have a near infrared and the far infrared near infrared means the part of the infrared spectrum that is closest to the visible light and far infrared means the part which is closer to the microwave regions and mid infrared obviously is between these two are the middle of that primary source of this infrared radiation is thermal which I will discuss in the next slide that is basically heat now this is radiation is produced by the motion of atoms and molecules in an object higher the temperature more the atoms and molecules move and more the infrared radiation is so any objects radiates radiation in the infrared regions even an ice cube actually it radiates infrared radiations so to give an idea humans add even normal body temperatures radiate most strongly in the infrared region that is why there are cameras developed to get images in the infrared spectrum and these cameras are very popular for the night photography and you know this most of the human beings at normal body temperature radiates strongly in infrared radiation at about 10 microns and in the image which is shown here in the left part of this figure is the basically the you know the areas which are red and yellow are this highest temperatures regions as you can see that on the other hand this right side pictures shows and night picture night image of a cat using infrared radiations yellow white areas are the warmest so yellow white is ice actually are at the very high radiation radiation coming from the ice and the purple regions are the coldest so this kind of imaging techniques are widely used for the photographies of in the night or even sometime in case of the other things. So I am going to show you the actual values of the infrared radiations wavelengths and the and the web numbers wavelengths are false in the region of 2.5 to 17 micron that means they are quite large even in compared to the visible visible so once are actually I know 400 to 800 nanometers so if you multiply this one with nanometers that means if you multiply with 10 to the power 3 so it is basically 250 to 1700 nanometers so sorry 2500 to 17000 nanometers that is much much higher than the visible and so corresponding web numbers are basically 4000 to 600 centimeter inverse these frequencies match frequencies of the covalent bonds basically in the material or in the molecules rather stretching in the fiber and they are in the bending vibrations so you have a covalent bond like carbon carbon or carbon hydrogen or carbon oxygen covalent bonds there the these frequencies actually match very well with the stretching and the bending vibration of those bonds so therefore one can determine the kind of bonds presents inside a covalent bonded material this is why it is very widely used for covalent bond molecules so infrared radiations are infrared spectroscopies normally used to tell you what type of bonds are present in the material and also some type of other structural information which will show you as you go along so to give an idea why does it lie as I said you this lies between visible and the microwave the frequencies actually falls in the region of 10 to the power 14 to the power 12 harsh and web lengths are about 10 to the power 4 to 10 to the power 6 or other 10 to the power 3 to the power 5 nanometers that is what we have seen and so therefore they talks about the molecular vibrations and this are indicate can be studied we have already discussed about you visible which can be used for valence electronic transitions and so IR is basically complementary technique as compared to the you visible now to give us better spot perspectives of this infrared spectroscopic process actually deals with quantum mechanical energy levels which are similar to the molecular vibrations so I do not have time rather to go into the quantum mechanical treatment of the molecular structure I hope you have already studied in your different courses like fixed metals are maybe some other quantum mechanical courses so I understand that these techniques are basically this was quantum mechanical treatment of molecules gives you the idea of the different quantum mechanical energies and we know that there are different quantum numbers starting from principle quantum numbers to magnetic quantum numbers to azimuthal quantum nostrils pin quantum numbers they indicate the different energy levels so and as in this case actually quantum mechanical energy levels which are used are other in higher spectroscopy are basically similar to the molecular vibrations now we perceive this vibration in terms of heats actually so that means some kind of heat that is why I showed you some pictures few minutes back where we can image the animals are even human using infrared camera when we say a covalent bond between two atom is of certain lengths we are citing an average because the bond behaves as there is a vibrating spring directly between atom let us see the picture here big atom the small atom the bond between these two actually can be thought of is basically like a spring spring or vibrating spring which is connecting them so that means molecules are vibrating in a certain manner as the atoms are vibrating in a molecule certain manner for simple molecule is a diameter molecule is you can very easily model this kind of situations using this picture so if that is the case that means I know we know that for any spring there is a vibration this frequency which is very unique to the spring and if we know the vibration frequency we can know the energy and if once you know the energy we can clearly say that if you use the infrared radiations we can analyze this spring to the higher level and when it comes back to the ground level it will emit the radiation which is absorbed and by that by measuring that we can determine type of bond presence in the molecule in the material so now you know as I said bonds between the atoms in a molecule can stretch can bend when it absorb infrared energy and that is how actually the infrared the whole plot between the infrared the between the absorption or the transmissions process wavelength can be prepared here so to give you some idea this is called systematic stretch I will show you some even nice videos systematic stretch means you have suppose oxygen that to harden atom this like water molecule so there will be systematic stretch in these two bonds oxygen hydrant bonds you can have even asymmetric stretch due to application of the infrared like this these two are different directions arrows or you can have bent that means you can have basically the hydrogen atoms actually can move little bit or other vibrate little bit this way and then that can create a pen so molecules such as water actually can absorb infrared light when vibration results in a molecular dipole moment change this is very important as per the infospectroscopic concern because that is how we can actually utilize this technique to determine what kind of particular you know vibration is present even in the water molecule itself to give you a better idea let us consider but then any kind of you know atomic energy levels and in the atom these are the ground states of vibrational ground version states you can clearly see these these are the atoms blue color atoms are stating there and these are the excited states now we apply certain wavelengths of infrared energy what is going to do these atoms which are present here they will absorb this okay and when they absorb they get to the excited states suppose they vibrate from mu 0 new 0 to me new one or even if you apply more energies for me one to me two okay so in as the time goes on these atoms which are excited to the mu one frequencies in can come back to the ground state and living behind in for radiations if you pump in more energy this atoms I can go into this energy states and the extra ten states and even then they can come back so when they will come back there will be huge change of energy and that returns you will come as a radiations and that is what has been written here absorption of basically occurs among the ground vibrational states in the energy difference and the corresponding spectrum determined by the specific molecular vibrations that is what is important the influence absorption is made energy green for the molecule and recorded as energy loss for the analysis beam so molecule absorb energy gain energy because it is absorbing from the infrared input radiation and as a result of which this energy loss in analysis beam that means the beam which is coming out from the material upright interaction will be there will be energy loss that can be determined easily yes as I said I will show you some very nice radios so as you can clearly see there are different types of states and bends stretch this all taken from Charles and Abrams which is this book classic book by these two authors as you can clearly see the stretch is basically symmetric where atoms can symmetrically move this is let me put you this is suppose carbon atoms and therefore hardened atoms and I am just putting two hardened atoms there and here and they are moving symmetrically so there is a symmetric stretch this is one kind of vibrations and this vibration will lead to certain kind of energy and vibration frequency also will be defined that is me 0 me 1 me 3 me 2 have so new and if you suppose these two bonds are moving opposite to each other at a particular time like when this one is moving out this is moving in so because of that there will be asymmetric vibrations that is also possible they are different states of energies okay so whenever radiation falls on it that can be it can modify this this kind of stretch of vibration along the line of the bond next one it can modify is the bent now you can have a different kind of bends the one which is shown as is basically in plane bent it can be either Caesar type or rocking type Caesar time means suppose in this case both the hardened atoms are moving in the same directions so therefore Caesar type is you know Caesar Caesar both the Caesar whenever we use a Caesar to cut certain things both these you know Caesar pieces they come and meet at the going the same directions other one is called rocking rocking means they are actually moving in the same opposite direction sorry in Caesar case these two atoms are moving in the opposite directions not in same direction that's why they can come a Caesar actually they come in opposite directions in a rocking case these two atoms are moving in the opposite directions one is sorry this top is more atoms are moving the same directions because they are moving the same direction there is a rocking aspects and these happens in the when the atoms are moving the same plane if the atoms are moving in the out of the plane so the first situations in this case like Caesar which correspond to twist okay that they will be twisting the bonds second one is called wag that is both the atoms are moving the same directions so that will lead to wag so you can clearly see that these are all shown here and Caesar is this like this and rocking is like this and this is I think twist so these situations will lead to different kinds of energy states of the molecule that's what I am trying to show up on so that you can you can actually use this kind of energy levels to detect the kind of vibration vibration is present in the molecule that's why it is called vibrational spectroscopy higher spectroscopy is always known as a vibrational spectroscopy to be greater you give you in better perspectives I spectroscopy process actually you know as a covalent bond oscillates due to oscillation of the dipole of the molecule okay so these two are actually dipole a varying electromagnetic field is produced and because of that you can see there is a propagation of the radiation and get the dipole mobile change the vibration and the more intense will be the electromagnetic field generated and electromagnetic field means there is vibration so that is what is normally is basically castically can be used now when a wave of infrared light encounters any oscillating electromagnetic field generated by this dipole of same frequency the two cup waves can couple and then when the two waves couple that means the IR radiation is coming and the electromagnetic field which is generated by this oscillating dipoles they can couple and when the couple actually these couple wave can vibrate with the double the amplitude of the initial wave that is what is shown here so you can see they are like this is the input and this is the because of the electromagnetic field and when the couple you have electromagnetic wave which is very very I know double the amplitude so this all can be direct used so this is again same things which I told you I am just going to rush you through this so these are all vibrations vibration means stretching of bonds spending of bonds internal rotations which I have shown you already and then vibration can change the dipole moment I have also showed you the asymmetrical stretching of bending I mean internal rotations this work as it can change the dipole moment of molecule symmetrical stretching of bending that is not normally so they are not active to the IR radiation now you know normally what the what is the kind of vibration level so wavelength I have already told you wavelength should be of the order of 2500 to 17 or 15 to 17 1000 nanometers okay now vibrations if you have vibration of suppose 4,100 and 11 centimeters inverse that is in stage case of H2 molecule so can you imagine how many vibrations can be done in per second it is very very large it can be of the order of 120 to the power 12 120 in 10 to the power 12 vibration per second that means one vibration per 10 to the power 15 seconds which is sometimes is very difficult to detect that is why you have auto-second laser spectroscopy you can where you can use infrared laser and using auto-second laser perspective you can determine each of these vibration or to second means ever minus 18 second so the spectroscopy which is done at the time scale can be used to detect this kind of vibrations which is now a routine nowadays many labs in this even our country has this kind of spectroscopies so this is a very large spectroscopy and now I have not told you about one thing this fine this vibration stretching everything is very fundamental to the eye spectroscopy this actually gets influenced by the mass mass of the molecule to give you some idea suppose this is a hydrogen molecule this is the iodine molecule hydro molecule molecular weight is 2 grams per mole and molecule for the iodine is 254 grams per mole huge huge molecule mass compared to the hydrogen now if you look at it the idea is get the mass while the wave number for the for the vibrations to happen this is also very important you must try to remember this so how much is the movement hook happens occurs in a vibration of the CC point now let us look at even this nitty-gitty sub-utils of that if I consider this suppose this is the one atom carbon atom this is another atom okay so if they vibrate approximately what is the you know length to which it can vibrate that is a distance actually distance approximately 10 picometers and the bond length is about 154 picometers that is what happens so for a CC bond with the bond length of 154 picometers 1 picometer is 10 to the power minus 12 meter because we know 1 nanometer is 10 to the power minus 9 meter so that means if the bond distance is a length is about 154 picometers so that means is equal to almost like 0.15 nanometers the vibration is even much much lower it's about 10 picometers so that is a distance scale I am talking about it that's for the stretching for the bending what is the bending angle well if we consider the carbon-carbon bonds bending angle is maximum 4 degrees so this much of bend happens when the molecule one of the carbon-carbon bonds actually vibrates and bends the 4 degrees and that's means distance about 4 or 10 picometers for CCC bonds angle is changes about 4 degrees is very difficult and these moves a carbon atom about 10 picometers so I will not discuss about these aspects because I have already discussed with you about energy and the web number and all things so let us look at even a big molecule like pentane okay pentane is C5H10 okay so there are five carbon atom one two three four five and then there are one two three four five six seven eight nine ten eleven twelve carbon atoms so if this is the case then what kind of type of vibration would occur in this big molecules for small molecules is easy okay examine this that can be done using by taking a spectrum this is pentane liquid and this measured using FTI you can see this is the absorbance absorptions this is the wave number and this is absorption a plotted have so you can see the pics coming in this picture the background and the pics coming in the pictures certain wave numbers the small pics there are big pics okay and by looking at this peak positions one can actually easily determine that kind of you know questions which have already asked that vibrations what kind of vibrations will take place in this molecule so increasing the absorption of higher radiation that means as you go point two to one absorptions what happens C is this is basically C is stretching and this is for so C is stretching and this is for C is bending to separate things because as you have seen here so I like to go back we have carbon so this is hydrogen this is carbon this is suppose carbon this is carbon hydrogen bond and this is carbon carbon bonds that is the overall picture in a pentane molecule so this is saturated what is called saturated polymer okay for alkene rather and so therefore if I look at it this is C is stretching this particular bonds which are coming the C is stretching and this is C is bending and that is what we can clearly see in case of the pentane now if you look at chloroform and even daughter chloroform chloroform is very common molecule this is taken from this source as you can see the chloroform is basically shown in the red and daughter chloroform is shown in blue so there certain frequencies of the vibrations we can see so what you can do is that in a chloroform you know chloroform is nothing but C is HCl3 that means there are one H and three scar chlorine bonds C is equal to CCl CCl CH there are two types of bonds so C is stretching for chloroform comes around 3002 this is this almost like this okay this part and C is bending C is bending comes 1120 so that is this and CCl comes around 700, 900, 800, 700, 700 and CCl bending comes 418 somewhere here comes this way sorry here it can be detected similarly for and these are the major values this are normally detected we can we observe we can see these things and for CdCl3 that is daughter chloroform okay these are the values and this we detect all of them so therefore one can actually clearly say from the measurements what kind of you know vibrational states of the bonds presents in the in this case the specific shift is because of H2D and that is because of mass increase so you can see that H2D because of that speak accepted this pick accepted this the set we discussed the mass increase means more mass means the peaks will come at a higher up numbers so lower web numbers not higher some more results so you know calculated values normally in this cases are had to be compared with computational values which are normally done using computational tools so so calculated values as is as I showed you here in this case calculated values are this and these are the major values so there is little bit of variations but still one can get this results very close to it on the of the measure value with the calculated value using better computational tools nowadays which is done and second thing is increasing the mass will shift the way numbers to lower values that's what I told you and third one stretching energies are always higher than the bending energies that we also learned and bending as you will be always other than the rotational international energies which can occur actually higher up lengths which is normally observe so therefore does this stretching relationship next question have to ask is the stretching relation energy have any relationship with the strength of the bond actually it is true in the true if you look at web number versus bond energies so bond energy is starting from 200 to about 600 kilojoule per mole web numbers 0 to 5000 as you can see that as the bond energy increases web number also increases so that means stretching energy is related to the strength of the bond as the bond increases bonds increases the stretching energy also increases that's what is us call plot at least resisting that's what is the case so we can plot it and you can get a very reasonable numbers of the confidence using R square well now we can actually go on looking at different kinds of molecules and do that most of them will be today's lecture will be of carbon type this is formal di added you know formal di added CHCl2 and this is first gene of this acetone we know that and so we will examine this carbonyl groups here so how does this CC CO bonds CO is double bonds here sorry this one everywhere you have a CO double bond everywhere you have a CO double bond that is in the all the cases so how does this CO stretching energy compare with these molecules here actually it's web number is 2053 in case of force then is it basically 1951 in case of acetone it's even higher 2063 centimeter inverse so that means depending on a structure formal aldehyde force gene or acetone the CO bond stretching energy will change that's understand it because the environment is changing the type of atoms present in the near the CO bonds as it changes the stretching energy also changes so carbonyl group normally has energies between 1700 to 3000 centimeter in now one can actually analyze different functional groups in organic compounds like atomics unlike atomic spectroscopy where the sharp energy transition occur due to well quantized electronegations molecular spectroscopy stances of bands we have seen that different kinds of stretching bands molecular vibrations are normally influenced by this surrounding groups we have seen one example in the last slides so let me just tell you in a brief what we can understand from this kind of spectroscopy this is stretching and bending energies and these are the web numbers so for a CH stretching energy a web number comes around 3000 but bending will come around 1000 to couple of hundreds OH that is in well groups the stretching energy can span from 4000 to about 2000 where are bending energy can span from about 1000 2500 to about 500 and then see oh see oh is see oh means see double bond oh that is the you know formula added acetone all this molecule has this kind of bonds there this is the stretching energy can span from 3000 to about 2500 and your what's called the other type of the see actually single bond can happen actually this stretching can happen even at lower web number that is 1200 to about 1000 and in this cases there are other things like CC double bonds this alkenes and it can happen in the range of about very close range about 1500 and then we can actually also have CC single bonds and this can happen even at much lower web numbers that is close to 1000 so using the eye spectroscopy actually one can determine these kind of bonds let's see that what else we can do so therefore we can actually identify different functional groups in the molecule that is very important to organic chemistry because you need to know what kind of functional groups present in the molecule which is produced by the chemical reactions and then only you can basically formula structure of the molecule special matching can be done by computer software as I told you even library spectroscopic data also available seen this this absorption follows Bias law we can actually do quantity analysis also I have only discussed you about Bias law in first lecture even in case of visible UV visible spectroscopy also how to apply that and one can actually use this law and then do quantity analysis also to do that let's see that okay and this is basically another kind of representation and you know I each I have told all these things already to you but let me reiterate each staging and bending vibrations actually occurs as very specific characteristic frequencies which we have already told you and as you can see that this actually where the field of electromagnetic field of accelerations interacts with the IR lights so transmission will be very low this is basically transmitted is important here not the absorption passes web number and region where these acceleration bonds interact with light the transmission is almost like 100% this is the once so that means there is no accelerations of bonds so there is no transmission this is again another kind of plots for transmissions buses web numbers and we can see different bands stretching and the bending bands we can determine that for different molecules and to give you some more ideas about it normally IR spectrums okay uses you need rather no evidence because web numbers are tightly proportional to the energies as we have told because is new is the energy and this can be written as AC by lambda so AC new bar is the energy say where new bar is basically the web number so wave number is directly proportional to the energy not the wavelength of Lama is inversely proportional to the energy that is why we plot it higher frequency higher numbers are required the higher energy so shorter blends equate the higher energy that is why we use the web numbers and web numbers are extensively use I do not want to tell detail about that so let me ask well to give you some more idea you know it is important to know that peak intensities actually are tend to be effects of the three factors one in the peak intensity is very strong that means peak is very tall and absorption is high as transmissions low medium ones with a peak is mid height that is not very tall and not be small also so where is in which this transmission is very small or you kind of weak and that means transmission is very high so as I if I go back to this plot I can show you there this is weak this is tall and the some cases you can see medium height here so all these things can see this this signals are available everywhere so and broad you can brought also then that the Gaussian distribution is abnormally brought this means actually more of the descending bond the spans have more energies exact transmittance values are rarely recorded here so that is why although we can apply the Beer's law but it is not you know good to use the exact transmittance to get good results or the quantity results from that okay so what else the infrared spectroscopy can do it can actually identify and quantify organic solids liquid gases it can analyze powders solids gels emulsions paste even pure liquids or solutions polymers and even pure and mixed gases so that means it can analyze everything solid liquid gas so that is why the versatility of this technique so important it can be used for all kinds of activities like quality control quality assurance even nowadays we actually as a scientist we use to detect different kinds of bonds presence samples sizes can be a single fibers like only 20 microns in lengths to even atmospheric pollutants nowadays people do a lot of study atmospheric pollutants so which can be large not only that it can be used in pharmaceutical research forensic investigations polymeric analysis which have showed you lubricant formulations and fuel additives lubricants which are used nowadays many of the many applications in the machine industry can be studied fuel additives you know in different fuels we add different kind of additives and whether they are stable in the fuel conditions can be studied that by this way food research is extensively used because food uses lot of different kinds of spices where this can be used their chemicals actually quality assurance which I have told you already environmental pollutions and the water pollutions can be studied by this way not only that biochemical research biomedical research can be done coatings surfactants can be studied they are all even either polymeric or even metallic or the ceramic materials many others most importantly they are used in the polymers well to give you all these things in our shell that in general the primary use of aspectoscope is detect the functional groups but it can be used because it leads to interaction of the electromagnetic spectrum with the actual bonds it can provide a quality probe of the functionality of the molecule because it can actually give different configurations it can actually give you different compression of the molecules present in the more in the in the material because one molecule can stretch paint or maybe you can have different kind of positions of the energy levels so that can be detected since most types of the bonds in covalent molecules have roughly the same energies like CC double bond or CO double bonds or CH or CH single bonds they show up in similar regions of the spectrum and you must remember that all the organic functional groups are made of multiple bonds therefore show up in the multiple IR bands that's how you see a band that means many peaks are there in one bands and in general so we can actually determine four regions OH NH CH single bonds they follow in this range triple bonds CC CN acetylene and the others to put as carbon nitrogen bonds 2005 700 2000 double bonds falls 2002 1600s at single bonds comes in the small wave numbers they are the higher energy so that is here that is you know CC CN or CO they come in the finger petrogens so that's why we use these techniques to determine all kinds of bonds.