How to Read and Interpret the IR Spectra | Step-by-Step Guide to IR Spectroscopy

Summary

في 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

00:00

🔬 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.

05:00

📈 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.

10:02

🧪 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.

Keywords

💡IR spectroscopy

IR spectroscopy، أو الطيف الأشعة تحت الحمراء، هو نوع من الطيف الشعاعي ويعتمد على التغييرات في الترددات لتشخيص المركبات الكيميائية. في الفيديو، يُستخدم لتفسير التفاعلات الحيوية والكشف عن المجموعة الوظيفية المختلفة في المركبات. على سبيل المثال، يُستخدم لتشخيص مجموعة الهيدروجين المرتبطة بالنيتروجين أو الأكسجين.

💡vibrational spectroscopy

vibrational spectroscopy هي نوع من الطيف الشعاعي يستخدم لدراسة الاهتزازات في الروابط الكيميائية. في الفيديو، يُعرف أن كل الروابط ت vibrate ويظهر هذا في الطيف الIR، مما يتيح لنا تحديد المجموعة الوظيفية في المركب.

💡functional groups

functional groups هي مجموعات كيميائية محددة تحدد خصائص المركب و起到重要作用 في IR spectroscopy. في الفيديو، يُستخدم لفهم التفاعلات التي تحدث عند التعرض للIR light وكيف يمكنها التعرف على المجموعة الوظيفية.

💡fingerprint region

fingerprint region هي منطقة في الطيف IR التي تقع تحت 1500 reciprocal cm وتحدد بدقة المركب. في الفيديو، يُذكر أنها مفيدة للتعرف على المركب من خلال المقارنة مع عينة معروفة، لكنها صعبة التفسير.

💡analytical region

analytical region هي منطقة في الطيف IR التي تقع فوق 1500 reciprocal cm وتتضمن الترددات التي نهتم بها في التحليل الكيميائي. في الفيديو، يُركز التركيز على هذا القسم لفهم المجموعة الوظيفية.

💡wave number

wave number هو الرقم الذي يُستخدم لوصف التردد في الطيف IR ويظهر مع التردد النووي. في الفيديو، يُستخدم لربط التردد النووي بالطاقة التي تُذبذب بها الروابط.

💡signal shape

signal shape هي شكل الإشارة في الطيف IR، يمكن أن يكون واسع و順 أو حاد وsharp. في الفيديو، يُستخدم لتمييز بين المجموعة الوظيفية، مثل الفرق بين O و NH.

💡signal strength

signal strength هي قوة الإشارة في الطيف IR التي يمكن أن تكون قوية أو متوسطة أو ضعيفة. في الفيديو، يُذكر أنها ليست الشيء الأكثر أهمية في التحليل، لكنها تعتمد على كيفية الحصول على الطيف.

💡reference table

reference table هي جدول يُستخدم لربط الترددات النووية مع المجموعة الوظيفية. في الفيديو، يُنصح بتعلم استخدام الجدول بشكل فعال لفهم الطيف IR.

💡practice

practice هي الخطوة الأساسية لتعلم التحليل الكيميائي IR. في الفيديو، يُشدد على أهمية ممارسة حل مسائل كثيرة لتكون قادرًا على تحليل الطيف IR.

💡fingerprint

fingerprint في سياق الطيف IR، يُستخدم للتعرف على المركب بشكل فريد من خلال التحقق في الإقليم الشخصي. في الفيديو، يُنصح بالحذر من الدخول إلى هذا الإقليم بدون معرفة ما تبحث عنه.

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