Students in the digital age expect to find information quickly and with minimal effort. As fledgling researchers, many have not yet learned how to select appropriate sources when conducting a literature search, especially when it comes to chemistry. While Wikipedia is a common source for students, I make sure students are aware of its limitations1,2. In my classroom, they are not allowed to cite Wikipedia as a primary source, though I recognize that they may use it in their initial explorations.

I’ve developed student activities to provide experiences in searching and assessing chemical information. There are several free (or at least, free to search) databases that are available on the web; some options are provided in Table 1, and others may be suggested by librarians or ACS resources.3,4 In some parts of the country, full access to databases and articles may be available through public libraries or school subscriptions.

As an introductory exercise, students are asked to access the databases and determine who owns or sponsors each site, and the scope of information that is indexed. The goal is to explore limitations that might exist, and to identify those sites that might provide relevant and useful information.

Database Access
Chemspider ( Free
Directory of Open Access Journals ( Free
EBSCOHost Subscribing public library or school
Google Scholar ( Free
JSTOR ( Free to search
Pubchem ( Free
Pubmed ( Free
ScienceDirect ( Free to search
Table 1. Databases
Sample Activity

To provide context for the exercise, I provide an article that addresses a chemistry topic that is relevant to a current lesson. Useful articles can be found in many sources, including Chemical and Engineering News, Chemistry World, and The New York Times (this is by no means a complete list). For example, an article published last October in The New York Times entitled, “New Climate-Friendlier Coolant Has a Catch: It’s Flammable,”5 was appropriate to use with a unit on atmospheric chemistry and hydrofluorocarbons (HFCs). This article describes a refrigerant — named only as “HFO-1234yf” — that is more expensive and has different flammability properties than traditional HFCs.

The students were asked to read the article and pretend that they had been asked to investigate this topic further to provide a technical summary to their research mentor. To begin the activity, students answer the following questions:

  1. In only 2-3 sentences, summarize what the article is about.
  2. What are the basic concepts that you need to understand in order to conduct more literature research on this topic? List any sections in your textbook that would be helpful.
  3. Understanding that HFC means “hydrofluorocarbon,” now determine the meaning of the acronym, HFO. List your source. List any other terms in the article that are unfamiliar to you, and look them up (and include your source).
  4. Which databases do you think will be most useful for finding relevant information? Explain your reasons.

These questions are important first steps to a more thorough search. Question 1 addresses an important skill in any literature research — concisely summarizing main ideas of a reference (which can lead into a discussion of annotated bibliographies). Sentence restrictions are important; by limiting the length, students must distill information and focus on key points. A typical response for question 1 might describe the development of a new controversial refrigerant that is expensive and flammable but with a lower impact on global warming.

Questions 2 and 3 help students frame the background knowledge and place the article in context; inexperienced searchers often cannot formulate good searches because they lack the basic vocabulary of the field. Simply typing “HFO” into a search engine will generate multiple hits; the unwary may decide that HFO means “heavy fuel oil” — the first hit that appears in Google (Figure 1) — rather than “hydrofluoroolefin.” Question 4 draws on the earlier exploration of different databases. As an example, JSTOR provides access to a variety of articles, but is more commonly used for research in the humanities and social sciences than in chemistry.

Figure 1. Google Search for HFO

Once students have made their predictions about useful databases, they test this by searching for “HFO-1234yf” on each database and recording the number of hits on each (Table 2).

One challenge in chemistry is that compounds may have multiple names — a trivial name, a systematic name, and a brand name. ChemSpider and PubChem provide the chemical name and structure; the formal name can also be used in searches. Interestingly, it limits the number of hits in all databases except for ScienceDirect; this allows for a discussion about how chemists would be more likely to use the formal name to describe compounds in the literature.

Database Hits: HFO-1234yf Hits: 2,3,3,3-Tetrafluoropropene
Chemspider 1a 1a 1 0
EBSCOHost 233 58
Google Scholar 2310 606
Pubchem 1b 1b
Pubmed 21 16
ScienceDirect 176 195
a. Trivial and chemical name lead to same entry; 2 primary articles are cited. b. Trivial and chemical name lead to same entry; 15 primary articles are cited.
Table 2. Database Hits
Crafting a Search Question

The final step in this exercise is to create a search question to yield a manageable number of hits. It should be apparent to the students that some databases are more useful than others. For one thing, it would be difficult to read 175 articles (let alone 2,300) in a timely fashion. A well-crafted search question, however, allows winnowing of the results to a manageable number. It must be emphasized that this initial culling of results is part of the process, rather than the destination. In some instances, five to ten reference articles may be sufficient for an assignment; in other cases, especially for multi-page papers or long-term research projects, this process may be repeated several times.

By this point, students should have identified one or two databases to use for a productive search, and decided to use the chemical name as well as the trivial name. Remember, the goal is not to amass the greatest number of sources, but to direct the preliminary search. A research question provides structure and limits for the search; otherwise the beginning researcher can quickly be overwhelmed by the sheer volume of hits. The question should be directed toward specific information. For example, “How safe is HFO-1234yf?” is very broad, whereas “How does the flammability of 2,3,3,3-tetrafluoropropene affect its safety?” is better.

Keywords can be generated from the question, and a simple list completed (Table 3A). The table is filled out by adding one to three possible synonyms (or alternative words) and related terms for each key concept (Table 3B). These terms can be both broader and narrower.

Concept #1 Concept #2 Concept #3 Concept #4 Concept #5
2,3,3,3-tetrafluoropropene Safety Flammable Fire Ignition
Table 3A. Keyword Generation

Concept #1 Concept #2 Concept #3 Concept #4 Concept #5
2,3,3,3-tetrafluoropropene Safety Flammable Fire Ignition
HFO-1234yf Unsafe Risky Inflammable Combustible Flame Spark Combustion
Table 3B. Keyword Expansion

If any of the keywords have different endings (e.g., verb tense, plural/singular nouns), truncation can be used to streamline a search. For example, the search “flam*” would capture “flammable,” and “flame,” while “ignit*” would retrieve hits containing “ignites,” “ignited,” “ignite,” “igniting,” and “ignition.”6 Students can also use Boolean operators (AND, NOT, OR) and parenthetical groupings to link different concepts together in a search statement, such as:

(“2,3,3,3-tetrafluoropropene” OR HFO-1234yf) AND flam* AND safe*

It’s a good idea to search both the common and chemical names; though some references might use both, many will use only one. The final search statement draws upon the original research question about the flammability and safety of HFO-1234yf.

This is good point at which to complete an in-class assignment, and send students home with their search statement. As a homework assignment, they can complete a search in one database, and identify a reasonable number of articles to begin their research. I direct my students to utilize our school’s subscription to ScienceDirect, but the choice of database can be left to the student or teacher. It’s not actually necessary that students obtain and read the articles, but they should justify their selection of four to six sources that they could use to investigate this topic further and provide a technical summary. As an illustration, the final search statement garnered only 50 hits in ScienceDirect (Table 4).

Search Terms Hits
HFO-1234yf 176
2,3,3,3-Tetrafluoropropene 195
2,3,3,3-Tetrafluoropropene OR HFO-1234yf 205
("2,3,3,3-Tetrafluoropropene" OR HFO-1234yf) AND flam* AND safe* 50
Table 4. ScienceDirect Hits

Though 50 papers still seem to be a lot of reading, it’s permissible — and desirable — to select only those that appear most relevant, either by title or abstract, for an initial survey. Thus, the 50 hits can be reduced to five promising articles (Table 5).

  1. P. Papas et al., Laminar flame speeds of 2,3,3,3-tetrafluoropropene mixtures. Proc. Combust. Inst. 36, 1145–1154 (2017).
  2. S. G. Davis, J. L. Pagliaro, T. F. Debold, M. van Wingerden, K. van Wingerden, Flammability and explosion characteristics of mildly flammable refrigerants. J. Loss Prev. Process Ind. (2017), doi:10.1016/j.jlp.2017.05.019.
  3. J. K. Vaghela, Comparative Evaluation of an Automobile Air - Conditioning System Using R134a and Its Alternative Refrigerants. Energy Procedia. 109, 153–160 (2017).
  4. Y. Lee, D. Kang, D. Jung, Performance of virtually non-flammable azeotropic HFO1234yf/HFC134a mixture for HFC134a applications. Int. J. Refrig. 36, 1203–1207 (2013).
  5. H. Zhang, C. Liu, X. Xu, Q. Li, Mechanism of thermal decomposition of HFO-1234yf by DFT study. Int. J. Refrig. 74, 399–411 (2017).

Table 5. Initial References

The goal of this exercise is to introduce students to efficient search strategies. The challenge is to convince them that the initial search is just a beginning, and that they may need to repeat the process several times for a single project.

  • 1 Mandler, M. D. Glaring Chemical Errors Persist for Years on Wikipedia. J. Chem. Educ., acs.jchemed.6b00478 (2017).
  • 2 Wilson, A.M., Likens, G. E. Content volatility of scientific topics in Wikipedia: A cautionary tale. PLoS One. 10(8), 10–14 (2015).
  • 3 Wilkinson, S. L. A guide to digital literature. Chem. Eng. News. 80(1), 30–33 (2002).
  • 4 Walker, M. A. Public Chemical Databases and the Semantic Web. In: ACS Symposium Series., 197–217 (2014).
  • 5 Hakim D. New Climate-Friendlier Coolant Has a Catch: It’s Flammable. New York Times, A20 (2016).
  • 6 Many libraries have detailed instructions on database searching, Boolean operators, and truncation. One example from MIT (