How to Read and Interpret the IR Spectra | Step-by-Step Guide to IR Spectroscopy
Summary
TLDRفي هذا النص، يُقدم مرشد في الكيمياء العضوية، فيكتور، تعليل عملي لتحليل الطيف الأشعي تحت الحمراء (IR) لفهم الروابط الحيوية في الجزيء. يُشرح الفرق بين الإقليم الشخصي والتحليلي في الطيف، ويشدد على أهمية الممارسة في حل مسائل الطيف لفهم الروابط المختلفة والتفاعلات بين الأشعة والفena. وينصح بالعمل على مجموعة واسعة من المشكلات ل擅习 التحليل الطيفي وفهم الإشارات التي تشير إلى المجموعة الوظيفية في الجزيء.
Takeaways
- 🌟 IR spectroscopy (Infrared spectroscopy) is a technique used to identify functional groups in molecules by analyzing the vibrations of bonds.
- 🔍 The video emphasizes practical application over theory, focusing on how to solve IR spectra and answer exam questions.
- 📈 Infrared spectra are divided into two regions: the fingerprint region below 1500 reciprocal cm and the analytical region above 1500 reciprocal cm.
- 🔑 The analytical region is the most important for identifying functional groups, while the fingerprint region is unique but difficult to interpret.
- 📊 Wave numbers, expressed in reciprocal centimeters, are directly related to the vibrational frequency and energy of the bonds.
- 📝 The shape of the signals in the IR spectrum, such as broad and smooth or spiky, provides clues to the type of functional groups present.
- 📉 Signal strength in the IR spectrum is less important as it can vary depending on how the spectrum was obtained.
- 📚 Reference tables are essential tools for matching observed wave numbers and signal shapes to known functional groups.
- 🎓 Memorizing common wave numbers and practicing with IR spectra is crucial for efficiently solving problems on exams.
- 🔬 The presence of specific signals, such as those for O-H, N-H, and C=O bonds, can indicate the type of functional groups in a molecule.
- 📝 Practice is key to mastering IR spectroscopy; solving multiple problems helps in recognizing patterns and improving speed.
Q & A
ما هو الIR spectroscopy؟
-الIR spectroscopy هو نوع من الطيفيات الكهرومغناطيسية التي تعتمد على الاهتزازات لتحليل المركبات الكيميائية. يستخدم هذا النوع من الطيفيات لرؤية الروابط التي ت vibrate وبما أن جميع الروابط ت vibrate، فمن الممكن مشاهدتها في الطيف الIR.
ما هي الفرق بين الanalytics region والfingerprint region في الIR spectroscopy؟
-الanalytics region هي النطاق الذي يقع فوق 1500 reciprocal cm ويحتوي على المعلومات التي نهتم بها، بينما fingerprint region يقع أسفل 1500 reciprocal cm ويتم استخدامه في التعرف على المركبات من خلال المقارنة مع عينات معروفة.
ما هي المعلومات التي يمكن الحصول عليها من region الIR التحليلي؟
-من المعلومات التي يمكن الحصول عليها من region الIR التحليلي هي الwave number، شكل الإشارة، وقوة الإشارة، مع أن الwave number والشكل هو أكثر المعلومات أهمية.
لماذا يعتمد الIR spectroscopy على الترددات المختلفة للكشف عن المجموعات الوظيفية المختلفة؟
-لأن المجموعات الوظيفية المختلفة تمتص الضوء عند ترددات مختلفة، يمكننا من خلال هذا الIR spectroscopy تحديد المجموعات الوظيفية الموجودة في الجزيء.
ما هي الأهمية الأساسية في الIR spectrum التي يجب ملاحظتها عند حل مسائل الIR؟
-الأهمية الأساسية هي الwave numbers وشكل الإشارة، حيث يمكن استخدامها لربط الإشارة مع مرجع المجموعة الوظيفية.
لماذا ينصح بممارسة حل مجموعة كبيرة من المشكلات في الIR spectroscopy؟
-الممارسة تعزز المعرفة العملية وتضمن القدرة على حل المشكلات بشكل أسرع وأكثر دقة، مما يساعد في تحسين الأداء في الاختبارات.
كيف يمكن استخدام مرجع المجموعة الوظيفية لحل مسائل الIR؟
-يمكن استخدام مرجع المجموعة الوظيفية لربط الwave numbers والشكل الإشارة مع المجموعات الوظيفية الموجودة في الIR spectrum.
ما هي الخطوات التي ينصح بها النص لحل الIR spectrum؟
-الخطوات هي: النظر من اليسار إلى اليمين في الIR spectrum، تحديد الwave numbers، مقارنة الشكل الإشارة مع مرجع المجموعة الوظيفية، واستخدام الIR كخطوة أولية في تحليل التركيب الكيميائي.
لماذا يمكن أن تختلف مظهر الإشارة في الIR spectrum من جذع لآخر؟
-قد يختلف مظهر الإشارة بسبب عوامل مثل طريقة الحصول على الطيف، نوع العينة، وطبيعة الجزيء.
كيف يمكن للIR spectroscopy مساعدة في تحديد التركيب الكامل للجزيء؟
-بعد تحديد المجموعات الوظيفية من خلال الIR، يمكن استخدام بيانات أخرى مثل الNMR لتحديد التركيب الكامل للجزيء.
Outlines
🔬 Introduction to Infrared Spectroscopy
Victor introduces the topic of infrared (IR) spectroscopy, emphasizing the practical aspect of the technique rather than delving into extensive theory. He explains that IR spectroscopy is a vibrational spectroscopy method used to identify different functional groups in molecules by observing their absorption of infrared light at specific frequencies. The video aims to teach viewers how to interpret IR spectra and solve related exam questions. Victor advises viewers to have a notebook ready to note important points and encourages them to use a reference table to match observed wave numbers with known functional groups.
📈 Understanding IR Spectrum Regions and Signal Characteristics
The script delves into the two main regions of an IR spectrum: the fingerprint region below 1500 reciprocal cm and the analytical region above it. The fingerprint region is unique to each molecule but difficult to interpret without expertise. The analytical region, which is the focus of the video, provides information about wave numbers, signal shapes, and signal strengths. Victor explains the significance of these features and how they can be used to identify functional groups in a molecule. He also discusses the importance of practice in mastering the interpretation of IR spectra and provides tips on how to use a reference table effectively.
🧪 Practical Approach to Solving IR Spectra Problems
Victor outlines a practical approach to solving IR spectra problems, starting from the left side of the spectrum and moving right. He highlights key regions to look for specific functional groups, such as O-H and N-H groups around 3500 reciprocal cm, C-H stretches around 3000, and triple and double bonds in the 2500 to 1500 reciprocal cm range. The video provides examples of how to interpret specific signals and match them with functional groups. Victor stresses the importance of practice and memorization of key wave numbers for efficient problem-solving. He also warns against relying solely on the fingerprint region without a solid understanding of the analytical region.
🎓 Mastering IR Spectroscopy Through Practice and Tips
In the concluding part of the script, Victor summarizes the key points covered in the video, including how to interpret wave numbers, signal shapes, and strengths in an IR spectrum. He reiterates the importance of practice and provides a challenge for viewers to solve multiple spectroscopy problems daily to improve their skills. Victor also encourages viewers to use the reference table effectively and to combine IR spectroscopy with other techniques like NMR for complete structural determination. He invites viewers to subscribe for more tutorials, engage with the content through likes and shares, and ask questions for further clarification.
Mindmap
Keywords
💡IR spectroscopy
💡vibrational spectroscopy
💡functional groups
💡fingerprint region
💡analytical region
💡wave number
💡signal shape
💡signal strength
💡reference table
💡practice
💡fingerprint
Highlights
Introduction to Infrared (IR) spectroscopy as a practical guide for solving IR spectra and exam questions.
IR spectroscopy is a vibrational spectroscopy technique that reveals the presence of different functional groups in a molecule through their absorption of IR light.
Explanation of the two regions in an IR spectrum: the fingerprint region below 1500 reciprocal cm and the analytical region above 1500 reciprocal cm.
The fingerprint region is unique for each molecule but difficult to interpret, making the analytical region the focus for identifying functional groups.
Importance of wave numbers in the analytical region, which are directly proportional to the vibrational frequency and energy of the bonds.
The significance of signal shape in identifying functional groups, such as broad and smooth for O-H groups and sharp for N-H groups.
Differentiation between signal strength (strong, medium, weak) and its dependence on the method of obtaining the spectrum.
The use of a reference table to match observed wave numbers and signal shapes to known functional groups.
Emphasis on the necessity of memorizing common wave numbers for efficient problem-solving during exams.
The approach to solving IR spectra by scanning from left to right, starting with the area around 3500 reciprocal cm for O and NH groups.
Identification of carbon-hydrogen stretches around 3000 reciprocal cm, with specific signals indicating sp3 and sp2 hybridization.
Recognition of triple bond signals in the range of 2500 to 2000 reciprocal cm, particularly for terminal triple bonds.
Analysis of double bond signals, such as C=O and C=C, in the region of 1800 to 1500 reciprocal cm.
Advice against relying solely on the fingerprint region without mastery of the analytical region, due to its complexity.
Examples of applying the learned techniques to interpret IR spectra and deduce the presence of specific functional groups.
The importance of combining IR spectroscopy with other techniques like NMR for complete structural determination of compounds.
Encouragement to practice solving spectroscopy problems daily to master the skill and prepare for exams.
A final summary of the key points covered in the video, including interpreting wave numbers, signal shapes, and strengths, and using a reference table.
A call to action for viewers to engage with the video by liking, sharing, and subscribing for more organic chemistry tutorials.
Transcripts
hey everyone Victor is here your guide
to All Things organic chemistry and
today I want to talk about the IR
spectroscopy and before you yawn at me
no this is not going to be one of those
videos where I bore you with 30 minutes
of theory no this video is going to be a
practical guide that will teach you
everything you need to know about the IR
with the emphasis on how to solve the IR
Spectra and answer the exam questions
which is exactly what you're going to be
tested on so grab your cup of coffee and
notebook to jot down the most important
parts hit the like button for good luck
on the test and let's get started IR
stands for infrared spectroscopy this is
a vibrational spectroscopy which means
that if something vibrates it is going
to be visible in the IR spectrum and
guess what all bonds vibrate there are
different types of vibrations and some
of those vibrations are visible in
so-called analytical region of the IR so
the idea is quite simple you Shine the
IR light at your molecule and different
functional groups will absorb that light
and since different bonds and functional
groups absorb light at different
frequencies we can tell exactly what we
have in our molecule so for instance on
this spectrum I have something that
absorbing light here here and here but
the question is what exactly does all of
that mean when it comes to the IR
spectrum we have two regions we have a
fingerprint region which is below 1500
reciprocal cm and we have the analytical
region above 1500 reciprocal cmet
anything we care about is going to be in
the analytical region right over here
the fingerprint region will only be
useful for you if you are trying to
identify your molecule by comparing it
to a known sample the fingerprint region
works well like a fingerprint it's
pretty much unique for each molecule
however it is nightmarishly difficult to
interpret unless you really know what
you're looking for so we'll leave this
to the pros and focus on the analytical
region of the spectrum so the
fingerprint region is something that we
don't really care about so what type of
information are we going to get from the
analytical region first of all the wave
number which is these numbers over here
it's typically expressed in reciprocal
centimeters and it's related to the
vibrational frequency which is directly
proportional to the energy with which
our bonds are vibrating so the higher
the wave number the higher the energy
with which the bond vibrates so for
instance on this spectrum I have a
couple of signals one at about 3,400
reciprocal cm and another one at around
2850 2950 in addition to the wave number
we'll also look at the signals shape so
like for instance this signal is Broad
and smooth while this one is very spiky
and finally the least bit of information
for us is going to be the signal
strength which can be strong if it deeps
down below 30% transmittance medium if
it is somewhere in the middle of the
transmittance scale and weak if the
signal is higher than 70 or so now the
signal strength is the least important
piece of information as the strength
will depend on how the Spectrum was
obtained and U what exactly the molecule
is all about this same molecule can have
differently looking signals in terms of
their strength depending if the Spectrum
was let's say obtained from the thin
film or potassium bromide mold or Nal
mix Etc what will be the same though is
the position of the signal and its shape
so once you get your wave numbers and
the shape you can matage those to the
reference table so for instance here is
the reference table I give to my
students this one visually represents
the position of the signals in the
Spectrum so it's kind of easy to match
what you are seeing in the Spectrum to
what we have on the table if you like
this one you can always download it from
organic chemistry tutor.com but I'm
pretty sure your textbook has something
similar to that well maybe not that
pretty or the reference table can be
given to you in the form of an actual
table I suggest you choose whichever
table works for you and learn how to use
it efficiently some people like the
visual one some people like the table
one whatever works will work for you
doesn't matter which table you choose
But whichever table you choose you got
to learn how to use it properly I'm not
going to tell you to memorize most
common numbers but I'm going to tell you
to memorize most common numbers here is
a deal though even if you are efficient
at finding your reference numbers and
know your IR table like the back of your
hand it is still going to take a few
seconds here and a few seconds there to
compare those numbers and and those
seconds will add up very quickly on the
test the good news though is that you'll
memorize those numbers anyways if you do
enough problems which brings me to the
most important point of this video you
must work through a ton of problems that
part is not optional if you want to be
able to solve these problems you need to
practice and when I say practice I mean
attempt to solve as many problems as you
can not watch somebody solving them
recognizing how someone solved a puzzle
and solving a puzzle yourself are two
huge differences but enough of me
renting here let's get back to our IR so
when I solve my IR Spectra I always look
at the Spectrum from left to right the
area around 3500 reciprocal CM typically
houses the O and NH groups so for
instance in this case we have a broad
and smooth signal which which is the O
group but how do I know it's not the NH
you might ask well uh that's where the
shape of the signals come into play the
O is typically Broad and smooth while
the NH is typically weaker and sharper
so here is the NH signal and how it
looks like for the comparison see it's
much weaker and much sharper than the O
group then we have this 3,000 line this
is a very important line in the IR
because this is where you normally see
your carbon hydrogen stretches signals
leaning onto the 3,000 from the right or
in other words signals that are hair
under 3000 so about 2950 or so are the
regular sp3 hybridized carbon hydren
stretches you should see those signals
for the majority of your compounds
signals leaning onto your 3,000 from the
left side or in other words signals that
are just a little bit over 3,000 like
3050 those are SP2 Hy hybridized carbon
hydrogen stretches so you'll expect to
see those guys if you have double Bonds
in your molecule and those double bonds
have hydrogens on them this molecule
doesn't have any so we are not seeing
anything there the next important region
we are going to look at is going to be
around 2500 to 2,000 reciprocal CM this
is where the triple bonds leave those
signals are typically pretty weak and
can sometimes completely disappear but
if it is a terminal triple bond like
what we have here here we are going to
have a sharp Spike at almost exactly
3300 CM which is the SP hybridized
carbon hydrant stretch it's a somewhat
rare signal since we are only going to
see it for the terminal triple bond but
nonetheless you should be familiar with
this signal the next important region is
the 18800 to 1500 CM which is where we
have various double bonds for instance
in this case I have a CO double bond at
roughly 1700 and I also have a cc double
bond at about 1650 these are of course
the most prominent functional groups
you'll be looking at in your molecule
there are many other ones that can
potentially pop up in the analytical
region and with practice you will learn
to recognize those as well with time and
practice you'll learn to recognize all
of these functional groups and will
memorize most of these numbers as well
you'll also be able to recognize some
signals in the fingerprint region but
unless you are comfortable with the
analytical region first which is above
1500 reciprocal CM don't even poke your
nose into the fingerprint you'll get
lost there and you will identify things
that are not in your molecule uh just
because you don't know what you're
looking for Beware of the fingerprint
and only go there if you really know
what to look for all right let's look at
a few examples here here I am not seeing
anything in the 3500 region so I do not
expect any o or NH groups next I'm
seeing these spikes uh leaning onto
3,000 from the right side this is the
indication of the regular sp3 hybridized
carbon hydren stretches we expect to see
those in the majority of our molecules
then I'm also seeing the carbonal co
double bond at about 1716 here which
means that we are most likely looking at
some sort of a ketone and while I can't
tell you the exact structure of your
molecule
I know what types of functional groups
to expect from this molecule so if I had
more data like let's say data from the
hydrogen NMR or carbon NMR I'd be able
to tell you what exactly I'm looking at
here in this molecule for instance I
have a broad smooth signal at 35 3300
which is a straight up indication of an
alcohol I'm also seeing some sp3
hybridized carbon hydren stretches at
the right about uh 3,000 reciprocal C CM
leaning on it from the right side and
that's about it which means that this
molecule is most likely some sort of
simple alcohol and here is another
example here I'm seeing some signals
from the SP2 hybridized carbon hydren
stretches because those signals are a
little bit above 3,000 I'm also seeing
the typical sp3 hybridized carbon
hydrogen stretches which I would be more
surprised if I didn't see honestly I'm
also seeing a carbonal at
1730 and there is also a tiny signal
over here for the carbon carbon aromatic
Bond So based on these data we can
conclude that this is likely an aromatic
Ketone or other type of a carbonal
looking at the fingerprint region I can
say that this is actually an aster but I
wouldn't expect a typical sophomore
organic chemistry student to be able to
fish out this information from the IR
alone so normally the IR will be the
first step in your spectroscopic
determination of a compound and you'll
be able to come up with the complete
structure using the combination of the
IR NMR and maybe some other techniques
as I've mentioned before signals can
look differently from Spectrum to
Spectrum and from molecule to molecule
so solving spectroscopy questions is a
bit of an art and you can only become
good at it if you do a ton of practice
all right folks in these past few
minutes we've journeyed through the
landscape of the IR spectroscopy
together decoding the hieroglyphics of
the Peaks and valys on those Spectra you
now know how to interpret the wave
numbers the shape of the signals and
even their strength to a certain extent
you've got your reference table either
from me or your textbook or some other
place and you've equipped with tips on
how to efficiently read the IR spectrum
based on the approach that I outlined in
this video but remember it's one thing
to be a spectator and another to be a
player in the field you learn learning
curve will only Skyrocket when you roll
up your sleeves and get down to solving
real world problems starting today take
up my challenge solve at least two to
three spectroscopy problems every single
day until your final exam you'll stumble
you'll scratch your head you'll get
frustrated but eventually you'll conquer
this skill by the time the big test
rolls around you'll handle those
spectroscopy questions like a pro and if
you found this video helpful don't
forget to hit that like button and share
it with your friends and classmates
every thumbs up is like a high five to
me for more daily organic chemistry
tutorials and solutions subscribe and
hit that notification Bell and if you
have questions or need further
clarification drop a comment below I
always love to hear from you guys thank
you for tuning in watch this video next
and I'll see you
tomorrow
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